#include <bits/stdc++.h>
using namespace std;
int main() {
	double x, score;
	cin >> x;
	if (x >= 90) {
		score = 4;
	} else if (x <= 60) {
		score = sqrt(x);
		if (score * 10 < 60) {
			score = 0;
		} else {
			score = sqrt(x);
			int(x) = score * 10;
			if (x >= 90) {
				score = 4;
			} else if (!x <= 60) {
				if (sqrt(x) * 10 < 60) {
					score = 0;
				}
			}
		}
	} else {
		score = 4 - (90 - x) * 0.1;
	}
	cout << fixed << setprecision(1) <<  score << endl;
	return 0;

}