#include<bits/stdc++.h>
using namespace std;
int main(){
	int a;
	float p;
	scanf("%d",&a);
	if (a>10){
		p=(a-10)*1.5+2.5;
		printf("%.2f",p);
	}
	else {
		p=2.5;
		printf("%.2f",p);
	}
	return 0;
}
/**************************************************************
	Problem: 1043
	User: xiaojingxuan
	Language: C++
	Result: Accepted
	Time:15 ms
	Memory:2076 kb
****************************************************************/