#include <algorithm>
#include <cmath>
#include <cstdio>
#include <deque>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>

using namespace std;

typedef long long ll;

#define MOD 1000000007

int calc(int n) {
  int res = 0;
  while (n) {
    res += (n % 10);
    n /= 10;
  }
  return res;
}

int main() {
  int n;
  cin >> n;
  int ans = n;
  for (int i = 1; i < 100; ++i) {
    ans = calc(ans);
  }
  cout << ans << endl;
  return 0;
}