#include<bits/stdc++.h>
using namespace std;
int main(){
	int n;
	float q;
	cin>>n;
	if (n<=10){
		q=2.5;
	}
	else{
		q=(n-10)*1.5+2.5;
	}
	printf("%。2f",q);
    return 0;
}
/**************************************************************
	Problem: 1043
	User: xiaojingxuan
	Language: C++
	Result: Wrong Answer
****************************************************************/