#include<bits/stdc++.h>
using namespace std;
int main(){
    int n;
    cin>>n;
    if(n<=10) cout<<n*2.5;
    if(n>10) cout<<10*2.5+10*1.5;
	return 0;
}
/**************************************************************
	Problem: 1043
	User: lijinkai
	Language: C++
	Result: Wrong Answer
****************************************************************/