#include<bits/stdc++.h>
using namespace std;
int main(){
	int a;
	float b;
	cin>>a;
	if(a<=10){
		b=2.5;	
	}else{
		b=(a-10)*1.5+2.5;	
	}
	printf("%.2f",b);
	return 0;
}
/**************************************************************
	Problem: 1043
	User: huanghao
	Language: C++
	Result: Accepted
	Time:22 ms
	Memory:2072 kb
****************************************************************/