#include <algorithm>
#include <cmath>
#include <cstdio>
#include <functional>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>
using namespace std;
using ll = long long;
int main() {
  ll n;
  cin >> n;
  for(int i = 0; i < 100; i++) {
    ll tmp = 0;
    while(n > 0) {
      tmp += n % 10;
      n /= 10;
    }
    n = tmp;
  }
  cout << n << endl;
  return 0;
}