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

int main() {
  int n;
  cin >> n;
  
  vector<int> a(100);
  a.at(0) = n;
  for(int i = 0; i < 99; i++){
    int k = a.at(i), sum = 0;
    while(k > 0){
      sum += k % 10;
      k /= 10;
    }
    a.at(i+1) = sum;
  }
  
  cout << a.at(99) << endl;
}