#include <bits/stdc++.h>
using namespace std;
int x;
int main(){
    cin>>x;
    if (x>=90)
        cout<<"4.0";
    else if (x>=60)
        cout<<4-(90-x)*0.1;
    else{
        int a=sqrt(x)*10;
        if (a<60)
            cout<<"0.0";
        else{
            if (a>=90)
                cout<<"4.0";
            else if (a>=60)
                cout<<4-(90-a)*0.1;
        }
    }
    return 0;
}