Fix input parsing bug

calc.py

@@ -9,9 +9,9 @@ except ValueError:
     exit(1)
 
 try:
-    operand2 = int(operand1)
+    operand2 = int(operand2)
 except ValueError:
-    print(operand1 + " is not a number!")
+    print(operand2 + " is not a number!")
     exit(1)
 
 print("Your result is:")