#include <bits/stdc++.h>
using namespace std;
#ifdef LOCAL
  #include "settings/debug.cpp"
  #define _GLIBCXX_DEBUG
#else
  #define Debug(...) void(0)
#endif
using ll = long long;
#define rep(i, n) for (int i = 0; i < (n); ++i)

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

int main() {
  int n;
  cin >> n;
  vector<int> a(1, n);
  rep(i, 100) {
    a.push_back(digsum(a.back()));
  }
  cout << a[100 - 1] << endl;
  return 0;
}