#include<bits/stdc++.h>
using namespace std;
int main(){
	float a,q;
	cin>>a;
	if(a<=10){
		printf("%.2f",2.5); 
	}
	if(a>10){
		q=a-10.0;
		q=q*1.5+2.5;
		printf("%.2f",q);    	
	}
	return 0;
}

/**************************************************************
	Problem: 1043
	User: huangcanwu
	Language: C++
	Result: Accepted
	Time:15 ms
	Memory:2072 kb
****************************************************************/