#include<bits/stdc++.h>
using namespace std;
int main(){
    int n;
    float i;
    cin>>n;
    if(n<=10){
    	i=n*2;
    }else{
    	i=n*2*0.9;
    }
    printf("%.1f",i);
}
/**************************************************************
	Problem: 1636
	User: wangyiyang
	Language: C++
	Result: Accepted
	Time:11 ms
	Memory:2072 kb
****************************************************************/