#include <bits/stdc++.h>
using namespace std;
using ll = long long;
template <class T> using vec = vector<T>;
template <class T> using vvec = vector<vec<T>>;

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    int N;
    cin >> N;
    
    auto digit = [&](int x){
        int res = 0;
        while(x){
            res += x%10;
            x /= 10;
        }
        return res;
    };

    int ans = N;
    for(int i=0;i<99;i++) ans = digit(ans);
    cout << ans << "\n";
}