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

int main(){
  string s; cin >> s;
  int ans = 0;
  for(int i = 0; i < s.size(); i++) ans += s[i]-'0';
  ans %= 9;
  if(ans==0) ans = 9;
  cout << ans << endl;
  return 0;
}