#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <cmath>
#include <numeric>
#include <utility>
#include <iomanip>

using namespace std;
using int64 = long long;

struct aaa{aaa(){cin.tie(nullptr); ios::sync_with_stdio(false); cout<<fixed<<setprecision(20);};}aaa;

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

    cout << ans << endl;
}