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

/**************************************************************
	Problem: 1043
	User: HUANGYIBO
	Language: C++
	Result: Accepted
	Time:16 ms
	Memory:2072 kb
****************************************************************/