let main = (standardInput) => {
  let lengthList = standardInput.split(" ");
  let input = Number.parseInt(lengthList[0]);

  function fib(n) {
    let first = 1,
      second = 1,
      result = 0;
    if (n === 0 || n === 1) {
      return 1;
    } else {
      for (let i = 1; i < n; i++) {
        result = first + second;
        first = second;
        second = result;
      }
      return result;
    }
  }
  console.log(fib(input));
};

main(require("fs").readFileSync("/dev/stdin", "UTF-8"));
