#include<bits/stdc++.h>
using namespace std;
int main(){
	float a;
	cin>>a;
	if(a>10){
		printf("%.1f",a*2*0.9);
	}else{
		printf("%.1f",a*2);
	}
	
	
} 
/**************************************************************
	Problem: 1636
	User: linzihang
	Language: C++
	Result: Accepted
	Time:12 ms
	Memory:2072 kb
****************************************************************/