#include <iostream>
#include <cassert>

using namespace std;

int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);

  int N; cin >> N;
  int cur = N;
  for (int i = 0; i < 99; i++) {
    int tmp = 0;
    while (cur > 0) {
      tmp += cur % 10;
      cur /= 10;
    }
    cur = tmp;
  }
  cout << cur << endl;
  return 0;
}