A simple calculator (that only does sums) in Dart

sums.dart

import 'dart:io';

void main() {
  print("First number: ");
  firstNumber = stdin.readLineSync();
  print("Reading...");
  sleep(Duration(seconds: 1));
  print("Done!");
  print("Second number: ");
  secondNumber = stdin.readLineSync();
  print("Reading...");
  sleep(Duration(seconds: 1));
  print("Done! Your result: ");
  totalSum = firstNumber + secondNumber;
  print(totalSum);
}