#include <bits/stdc++.h>

using namespace std;

using ll = long long;

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    ll n;
    cin >> n;

    string s = to_string(n);

    for (int i = 0; i < 100; ++i)
    {
        ll a{ 0 };
        if (s.size() > 1)
        {
            for (size_t j = 0; j < s.size(); ++j)
                a += stoll(s.substr(j, 1));
        }
        else
            break;

        s = to_string(a);
    }
    cout << s << "\n";

    return 0;
}