function main(input) {
  const N = parseInt(input.trim());
  const a_1 = N;
  let a_i = a_1;
  for (let i = 2; i <= 100; i++) {
  	a_i = String(a_i).split("").map(Number).reduce((sum, num) => sum + num, 0);
  }
  const a_100 = a_i;
  return String(a_100);
}

// Don't edit this line!
console.log(main(require("fs").readFileSync("/dev/stdin", "utf8")));