function factorial(n) {
  let answer = 1;
  if (n == 0 || n == 1) {
    return answer;
  } else {
    for (var i = n; i >= 1; i--) {
      answer = answer * i;
    }
    return answer;
  }  
}

let n = 4;
answer = factorial(n);

console.log("The factorial of " + n + " is " + answer);