// write your code here cpp
#include<iostream>
#include<string>
using namespace std;

int main() {
    string str;
    int num = 0;
    while (cin >> str) {
        for (int i = 0; i < str.size(); i++) {
            num += str[i] - '0';
        }
        int sum = 0;
        while (num) {
            sum += num % 10;
            num = num / 10;
            if (num == 0 && sum / 10 != 0) {
                num = sum;
                sum = 0;
            }
        }
        cout << sum << endl;
    }
    return 0;
}