#include <bits/stdc++.h>
#define int long long
using namespace std;
double n;
signed main(){
	cin>>n;
	if(n>=90)cout<<"4.0"<<endl;
	else if(n<36)cout<<"0.0"<<endl;
	else{
		n=floor(sqrt(n)*10);
		n=4.0-(90.0-n)*0.1;
		cout<<fixed<<setprecision(1)<<n<<endl;
	}
	return 0;
}