#include <bits/stdc++.h>
#define rep(i, ss, ee) for (int i = ss; i < ee; ++i)
using namespace std;

void solve() {
  string s;
  cin >> s;
  unsigned cnt = 0;
  while (s.size() > 1 && cnt < 100) {
    unsigned sum = 0;
    for (auto c : s) sum += c - '0';
    s = to_string(sum);
    cnt++;
  }
  cout << s << endl;
}

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  solve();
  getchar();
}