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

int main(){
  int N;
  cin >> N;
  
  for(int i = 0; i < 100; i++){
    int sum = 0;
    while(N > 0){
      sum += N % 10;
      N /= 10;
    }
    N = sum;
  }
  
  cout << N << endl;
}