#include<bits/stdc++.h>
using namespace std;
int main()
{
	
	//11 2.5 + 1 * 1.5
	// 2.5+1 . 1.5
	int a;
	float result;
	cin>> a;
	if(a>10){
		result=2.5+(a-10)*1.5;
	}else{
		result=2.5;
	}
    printf("%.2f",result);
	return 0;
}

/**************************************************************
	Problem: 1043
	User: ct001
	Language: C++
	Result: Accepted
	Time:14 ms
	Memory:2072 kb
****************************************************************/