diff --git a/joseph_program.py b/joseph_program.py
index 4b6a7f2..41ac1fe 100644
--- a/joseph_program.py
+++ b/joseph_program.py
@@ -1,23 +1,24 @@
 import sys
 
-#!/usr/bin/env python3
-
 def main():
-    if len(sys.argv) >= 3:
-        a, b ,c = sys.argv[1], sys.argv[2]
+    # accept exactly two command-line arguments, or prompt interactively
+    if len(sys.argv) == 3:
+        a, b = sys.argv[1], sys.argv[2]
+    elif len(sys.argv) > 3:
+        print(f"Usage: {sys.argv[0]} <num1> <num2>")
+        sys.exit(2)
     else:
         a = input("Enter first number: ")
         b = input("Enter second number: ")
-        c = input("Enter third number: ")
+
     try:
         a_num = float(a)
         b_num = float(b)
-        c_num = float(c)
     except ValueError:
         print("Invalid number input.")
         sys.exit(1)
 
-    result = a_num + b_num + c_num
+    result = a_num + b_num
     # print as int when it's a whole number
     if result.is_integer():
         result = int(result)