#include <bits/stdc++.h>
using namespace std;
typedef long long ll;

ll func(ll x) {
    ll sum = 0;
    while(x > 0) {
        sum += x % 10;
        x /= 10;
    }
    return sum;
}

int main() {
    ll ans;
    cin >> ans;
    for(int i = 0; i < 100; ++i) {
        ans = func(ans);
    }
    cout << ans << endl;
    return 0;
}