#include<bits/stdc++.h>

using namespace std;

signed main(){
	int x;
	cin>>x;
	if(x>=90)cout<<fixed<<setprecision(1)<<4.0;
	else if(x>=60&&x<=89)cout<<fixed<<setprecision(1)<<double(4.0-(90.0-x*1.0)*0.1);
	else{
		int g;
		g = double(sqrt(x)*10.0);
		if(g<=60)cout<<fixed<<setprecision(1)<<0.0;
		else {
			cout<<fixed<<setprecision(1)<<double(4.0-(90.0-x*1.0)*0.1);
		}
	}

	return 0;
}