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

int main() {
	int D;
	cin >> D;
	if (D < 10) cout << D << endl;
	else {
		int X = (D - 10) / 2 + 10;
		if (D % 2 == 0) cout << X / 10 << endl;
		else cout << X % 10 << endl;
	}
}