#include<bits/stdc++.h>
using namespace std;
int main(){
	int n;
	float q;
	cin>>n;
	if(n<=10){
		q=n*2;
		printf("%.1f",q);
	}else{
		q=n*2*0.9;
		printf("%.1f",q);
	}
	
}

/**************************************************************
	Problem: 1636
	User: zhengzihao3
	Language: C++
	Result: Accepted
	Time:18 ms
	Memory:2072 kb
****************************************************************/