Update README.md

README.md

@@ -11111,7 +11111,7 @@ fn math(input: &str) -> i32 {
     if !input.chars().all(|character| OKAY_CHARACTERS.contains(character)) ||
        !input.chars().take(2).any(|character| character.is_numeric())
     {
-        panic!("Please only input numbers, +-, or spaces");
+        panic!("Please only input numbers, +-, or spaces.");
     }
 
     let input = input.trim_end_matches(|x| "+- ".contains(x)).chars().filter(|x| *x != ' ').collect::<String>(); // Remove + and - at the end, and all spaces