#define _USE_MATH_DEFINES
#include  <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
#include <string>
#include<math.h>
#include<iomanip>
#include<stdio.h>
#include <stdlib.h>
#include<stdio.h>
#include <queue>
#include<map>
#include <sstream>
#include<set>
#include<stack>
#include<time.h>
#include <sys/types.h>
#include <tuple>
#include <numeric>


typedef long long int ll;
//#include<bits/stdc++.h>


using namespace std;







int main()
{

    int Q;
    Q = 1;
    //cin >> Q;

    while (Q--) {
        int n;
        cin >> n;
        for (int i = 0; i < 100; i++) {
            int t = n;
            int a = 0;
            while (t) {
                a += t % 10;
                t /= 10;
            }
            n = a;

        }
        cout << n << endl;

    }
    return 0;
}