#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <utility>
#include <map>
#include <queue>
#include <cmath>
using namespace std;
typedef long long ll;
#define rep(i,n) for (int i=0;i < (int)(n);i++)

int main(){
  int n;
  cin >> n;
  for (int i = 0;i < 99;i++){
    string t = to_string(n);
    int res = 0;
    rep(i,t.size()){
      res += stoi(t.substr(i,1));
    }
    n = res;
  }
  cout << n << endl;
  return 0;
}