#include <bits/stdc++.h>
using namespace std;

int main() {
    int n; cin >> n;
    if (n < 10) {
        cout << n << endl;
    } else {
        n -= 9;
        int s = (n+1) / 2 + 9;
        if (n % 2 == 0) {
            cout << s%10 << endl;
        } else {
            cout << s/10 << endl;
        }
    }
    return 0;
}