P96965

#include <iostream>
using namespace std;

int sum_digits(int n) {

  int r = 0;
  while (n > 0) {

    r = r + (n%10);
    n = n/10;
  }
  if (r < 10) return r;
  else return sum_digits(r);
}

int reduction_of_digits(int x) {

  if (x < 10) return x;
  else {

    int z = sum_digits(x);
    return z;
  }
}

int main() {

  int x;
  while (cin >> x) {

    cout << reduction_of_digits(x) << endl;
  }
}