#include <iostream>
#include <sstream>

using namespace std;


int calc(string s)
{
    int ans = 0;
    for (int i = 0; i < s.length(); i++) {
        int num = (int)(s[i] - '0');
        ans += num;
    }
    return ans;
}

int main()
{
    string a;
    cin >> a;
    int ans;
    ans = calc(a);
    for (int i = 1 ; i < 100; i++) {
        ans = calc(to_string(ans));
    }

    cout << ans << endl;

}