/**
*    author:  boutarou
*    created: 14.08.2020 21:18:27
**/

#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i = 0; i < int(n); i++)
using ll = long long;
using P = pair<int, int>;

long long digit(long long x) {
    long long cnt = 0;
    while (x > 0) {
        cnt += x % 10;
        x /= 10;
    }
    return cnt;
}

int main() {
    ll n;
    cin >> n;
    rep(i,99) {
        n = digit(n);
    }
    cout << n << endl;

    return 0;
}