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

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