diff --git a/index.js b/index.js
index 3bb4d07..c96c045 100644
--- a/index.js
+++ b/index.js
@@ -4,7 +4,34 @@
  * 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;