#include <bits/stdc++.h>
using namespace std;
using namespace chrono;
#if __has_include(<atcoder/all>)
#include <atcoder/all>
using namespace atcoder;
#endif

int main() {
    int64_t n;
    cin >> n;

    auto f = [](int64_t x) -> int64_t {
        int64_t ret = 0;
        for (; x; x /= 10) {
            ret += x % 10;
        }
        return ret;
    };

    for (int64_t i = 0; i < 99; i++) {
        n = f(n);
    }

    cout << n << endl;

    return 0;
}