feat: print a reasonable number of significant digits

src/main.rs

@@ -22,5 +22,16 @@ fn main() {
         }
     };
 
-    println!("{:.3}", parse_and_calc(&input));
+    let result = parse_and_calc(&input);
+
+    let result_raw_string = format!("{}", result);
+    let mut significant_digits = result_raw_string.len() - 1;
+    for (i, _) in result_raw_string.char_indices() {
+        if !result_raw_string[i..result_raw_string.len()].contains(|c| matches!(c, '1'..'9')) {
+            significant_digits = i;
+            break;
+        }
+    }
+
+    println!("{result:.significant_digits$}");
 }