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

int main(){
    int n;
    cin>>n;
    if(n>=90){
        cout<<"4.0"<<endl;
        return 0;
    }else if(n>=60){
        printf("%.1lf",4.0-((90-n)*0.1));
    }else{
        if(sqrt(n)*10>=60){
            printf("%.1lf",4.0-(((90-ceil((sqrt(n)*10)))*0.1)));
        }else{
            cout<<"0.0";
        }
    }
    return 0;
}