#include<bits/stdc++.h>
using namespace std;
int main(){
	int n;
	float q;
	cin>>n;
	if(n<=10){
		q=n*1.5;
		cout<<q;
	}
	if(n>10){
		q=(n-10)*2.5+10*1.5;
		cout<<q;
	}
	
} 

/**************************************************************
	Problem: 1052
	User: zhengzihao3
	Language: C++
	Result: Wrong Answer
****************************************************************/