#include<bits/stdc++.h>
using namespace std;
int main(){
    int a;
    float q;
    cin>>a;
    if(a<=10)
    {
    	q=2.5;
    }else{
    	q=(a-10)*1.5+2.5;
    }
    printf("%.2f",q);
}

/**************************************************************
	Problem: 1043
	User: xuezihong1
	Language: C++
	Result: Accepted
	Time:17 ms
	Memory:2072 kb
****************************************************************/