#include<bits/stdc++.h>
using namespace std;
int main() {
	float s,q;
	cin>>s;
	if(s>10){
		q=2*10+((s-10)*2);
		q=q*0.9;
	}
	else{
		q=s*2;
	}
	printf("%.1f",q);
    return 0;
}

/**************************************************************
	Problem: 1636
	User: huangcanwu
	Language: C++
	Result: Accepted
	Time:11 ms
	Memory:2072 kb
****************************************************************/