#include <bits/stdc++.h>
using namespace std;
int main(){
	int a;
	float b;
	cin>>a;
	if(a>=10){
		b=a*2*0.9;
	}else{
		b=a*2;
	}
	printf("%.1f",b);
}
/**************************************************************
	Problem: 1636
	User: tonghuawei
	Language: C++
	Result: Wrong Answer
****************************************************************/