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

int64_t f(int64_t n)
{
  int64_t ret = 0;
  while (n > 0)
  {
    ret += n % 10;
    n /= 10;
  }
  return ret;
}

int main()
{
  int64_t N;
  cin >> N;
  for (int i = 0; i < 100; i++)
  {
    N = f(N);
  }
  cout << N << endl;
}