#include<bits/stdc++.h>

using namespace std;
using ll = long long;


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