#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const ll mod = 1000000007;
const int INF = 1001001001;

int main(){
    int n; cin >> n;
    for(int i = 0; i < 100; i++){
        int tmp = 0;
        while(n){
            tmp += n % 10;
            n /= 10;
        }
        n = tmp;
        //cout << tmp << endl;
    }
    cout << n << endl;
}