#include <bits/stdc++.h>

using ll = long long;
using namespace std;
const int INFint = 1e9+1;
const ll INFll = (ll)1e18+1;
ll MOD=1e9+7;


int main(){
  string s;
  cin>>s;
  //int N = int(s.size());
  for(int i(0);i<100;i++){
    int tmp(0);
    for(int j(0);j<int(s.size());j++){
      tmp += s[j]-'0';
    }
    s = to_string(tmp);
  }
  cout<< s << endl;
  return 0;
}