#include <bits/stdc++.h>
using namespace std;

#define ll long long
#define rep(i, n) for (int i = 0; i < (n); i++)
#define P pair<int, int>

int digit_sum(int x) {
  int res = 0;
  while (x > 0) {
    res += x%10;
    x /= 10;
  }
  return res;
}
int main() {
  int n;
  cin >> n;
  rep(i,100) n = digit_sum(n);
  cout << n << endl;


}