#include <bits/stdc++.h>
#define rep(i,s,n) for (int i = s; i < (n); ++i)
using namespace std;
using ll = long long;
using P = pair<int,int>;
using field = vector<vector<int>>;

int main() {
  int a;
  cin >> a;
  rep(i,0,100) {
    int b = 0;
    int t = a;
    while (t > 0) {
      b += t % 10;
      t /= 10;
    }
    a = b;
  }
  cout << a << endl;
  return 0;
}