#include<bits/stdc++.h>
using namespace std;
int main(){
	int n;
	cin>>n;
	if(n>=30) printf("%.1f",n*1.0);
    else (n>20&&n<=29) printf("%.1f",n*1.5);
	else if(n>=10&&n<=19) printf("%.1f",1.5*n)
	else  printf("%.1f",1.5*n)
	

	return 0;
}
/**************************************************************
	Problem: 1304
	User: linyuhang
	Language: C++
	Result: Compile Error
****************************************************************/