#include <bits/stdc++.h>
using namespace std;
int main(){
	float n,m;
	cin>>n;
	if(n<=20)m=n*1.68; 
	else m=n*1.98;
	printf("%.2f",m);
	return 0;
}
/**************************************************************
	Problem: 1643
	User: panyuchen
	Language: C++
	Result: Accepted
	Time:14 ms
	Memory:2072 kb
****************************************************************/