#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef vector<long long> vl;
typedef vector<bool> vb;
typedef vector<char> vc;
#define INF __INT32_MAX__
#define LINF __LONG_LONG_MAX__

int main() {
    int N; cin >> N;

    vi A(100);
    A[0] = N;
    for (int i = 1; i < 100; i++) {
        int x = A[i - 1];
        int sum = 0;
        while (x > 0) {
            sum += x % 10;
            x /= 10;
        }
        A[i] = sum;
    }

    cout << A[99] << endl;
}