#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);  
	return 0;
}

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