// #define _GLIBCXX_DEBUG
#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); ++i)
int digitSum(int n) {
    int ret = 0;
    while (n != 0) ret += n % 10, n /= 10;
    return ret;
}
int main() {
    // Input
    int N;
    cin >> N;

    // Calculation
    int a[101];
    a[1] = N;
    for (int i = 2; i <= 100; ++i) a[i] = digitSum(a[i - 1]);

    // Output
    cout << a[100] << endl;
}