diff --git a/tests/template/data/countdown/train.jsonl b/tests/template/data/countdown/train.jsonl
index 3e9adf0092..9329509906 100644
--- a/tests/template/data/countdown/train.jsonl
+++ b/tests/template/data/countdown/train.jsonl
@@ -14,3 +14,4 @@
 {"question": "A conversation between User and Assistant. The user asks a question, and the Assistant solves it. The assistant first thinks about the reasoning process in the mind and then provides the user with the answer.\nUser: Using the numbers [19, 25, 89], create an equation that equals 95. You can use basic arithmetic operations (+, -, *, /) and each number can only be used once. Show your work in <think> </think> tags. And return the final answer in <answer> </answer> tags, for example <answer> (1 + 2) / 3 </answer>.\nAssistant: Let me solve this step by step.\n<think>", "answer": "{\"numbers\": [19, 25, 89], \"target\": 95}"}
 {"question": "A conversation between User and Assistant. The user asks a question, and the Assistant solves it. The assistant first thinks about the reasoning process in the mind and then provides the user with the answer.\nUser: Using the numbers [8, 62, 43], create an equation that equals 27. You can use basic arithmetic operations (+, -, *, /) and each number can only be used once. Show your work in <think> </think> tags. And return the final answer in <answer> </answer> tags, for example <answer> (1 + 2) / 3 </answer>.\nAssistant: Let me solve this step by step.\n<think>", "answer": "{\"numbers\": [8, 62, 43], \"target\": 27}"}
 {"question": "A conversation between User and Assistant. The user asks a question, and the Assistant solves it. The assistant first thinks about the reasoning process in the mind and then provides the user with the answer.\nUser: Using the numbers [74, 5, 20, 88], create an equation that equals 50. You can use basic arithmetic operations (+, -, *, /) and each number can only be used once. Show your work in <think> </think> tags. And return the final answer in <answer> </answer> tags, for example <answer> (1 + 2) / 3 </answer>.\nAssistant: Let me solve this step by step.\n<think>", "answer": "{\"numbers\": [74, 5, 20, 88], \"target\": 50}"}
+{"question": "A conversation between User and Assistant. The user asks a question, and the Assistant solves it. The assistant first thinks about the reasoning process in the mind and then provides the user with the answer.\nUser: Using the numbers [15, 51, 73], create an equation that equals 37. You can use basic arithmetic operations (+, -, *, /) and each number can only be used once. Show your work in <think> </think> tags. And return the final answer in <answer> </answer> tags, for example <answer> (1 + 2) / 3 </answer>.\nAssistant: Let me solve this step by step.\n<think>", "answer": "{\"numbers\": [15, 51, 73], \"target\": 37}"}
diff --git a/tests/tools.py b/tests/tools.py
index 2bbb8c8931..46d6b4859b 100644
--- a/tests/tools.py
+++ b/tests/tools.py
@@ -42,7 +42,7 @@ def get_checkpoint_path() -> str:
 def get_unittest_dataset_config(
     dataset_name: str = "countdown", split: str = "train"
 ) -> StorageConfig:
-    """Countdown dataset with 16 samples."""
+    """Countdown dataset with 17 samples."""
     if dataset_name == "countdown" or dataset_name == "copy_countdown":
         return StorageConfig(
             name=dataset_name,
diff --git a/trinity/buffer/reader/file_reader.py b/trinity/buffer/reader/file_reader.py
index 50727641c6..0812c64ed9 100644
--- a/trinity/buffer/reader/file_reader.py
+++ b/trinity/buffer/reader/file_reader.py
@@ -26,12 +26,14 @@ def __init__(
         name: str,
         max_epoch: int = 1,
         offset: int = 0,
+        drop_last: bool = True,
     ):
         self.dataset = dataset
         self.dataset_size = len(dataset)
         self.name = name
         self.current_batch_size = None
         self.max_epoch = max_epoch
+        self.drop_last = drop_last
         if offset >= self.dataset_size:
             self.current_epoch = offset // self.dataset_size
             self.current_offset = offset % self.dataset_size
@@ -70,7 +72,7 @@ def read_batch(self, batch_size: int) -> List:
                 self.current_offset = 0
 
                 if self.current_epoch >= self.max_epoch:
-                    if len(batch) > 0:
+                    if not self.drop_last and len(batch) > 0:
                         return batch
                     else:
                         self.progress_bar.close()
@@ -96,6 +98,7 @@ def __init__(self, meta: StorageConfig, config: BufferConfig):
             load_dataset(meta.path, name=subset_name, split=self.split, trust_remote_code=True),
             name=meta.name,
             max_epoch=meta.total_epochs,
+            drop_last=True,
         )  # TODO: support resume
         self.tokenizer = transformers.AutoTokenizer.from_pretrained(config.tokenizer_path)
 
@@ -174,6 +177,7 @@ def __init__(self, meta: StorageConfig, config: BufferConfig):
             load_dataset(meta.path, name=subset_name, split=self.split, trust_remote_code=True),
             name=meta.name,
             max_epoch=meta.total_epochs,
+            drop_last=True,
         )  # TODO: support resume
         self.tokenizer = transformers.AutoTokenizer.from_pretrained(config.tokenizer_path)
 
@@ -248,6 +252,7 @@ def __init__(self, meta: StorageConfig, config: BufferConfig):
             name=meta.name,
             max_epoch=self.meta.total_epochs if meta.task_type == TaskType.EXPLORE else 1,
             offset=self.meta.index,
+            drop_last=self.meta.task_type == TaskType.EXPLORE,
         )
         self.read_batch_size = config.batch_size
         self.prompt_key = meta.format.prompt_key