diff --git a/index.js b/index.js
index 3bb4d07..ac621d0 100644
--- a/index.js
+++ b/index.js
@@ -4,7 +4,33 @@
  * Depending on the operation, either add up all of the numbers or subtract all of the numbers, from left to right.
  * @returns {number} The result of either adding all numbers or subtracting all numbers, depending on the arguments added to the command line.
  */
-function calculator() {}
+function calculator() {
+    let result = 0;
+    if(process.argv.length < 3) {
+    return  'No operation provided...'
+    }
+    else if(!process.argv[3]) {
+    return 'No numbers provided...'
+    }
+    
+    if (process.argv[2] === 'plus') {
+    for(let i = 3; i < process.argv.length; i++) {
+    result += Number(process.argv[i])
+    }
+    return result
+    }
+    if (process.argv[2] === 'minus') {
+    result = process.argv[3]
+    for(let i = 4; i < process.argv.length; i++) {
+    result -= Number(process.argv[i]);
+    }
+    return result
+    }
+    else {
+    return `Invalid operation: ${process.argv[2]}`
+    }
+    
+}
 
 // Don't change anything below this line.
 module.exports = calculator;