How to understand the maskRCNN config about the max_iter ?

[HuangChiEn]

it's hard to understand the config of maskrcnn :

DATASETS:
  TRAIN: ("coco_2017_train",)
  TEST: ("coco_2017_val",)

SOLVER:
  IMS_PER_BATCH: 16
  BASE_LR: 0.02
  STEPS: (60000, 80000)
  MAX_ITER: 90000

Since, coco_2017_train have 118000 images in used during training, then how could this config valid ?
epoch = MAX_ITER * IMS_PER_BATCH / 118000
i try to figure out how many epoch will it run, but this equation seems can not be solved. It seems only run 12 epoch.

Any suggestion will be appreciated !!