#include <bits/stdc++.h>
#define all(x) begin(x), end(x)

using namespace std;
using ll = long long;

int get_cnt(int x) {
    int ans = 0;
    while (x > 0) {
        ans += x % 10;
        x /= 10;
    }
    return ans;
}

int main() {
    int x;
    cin >> x;
    while (x >= 10) {
        x = get_cnt(x);
    }
    cout << x << '\n';4
}