#include<bits/stdc++.h>
using namespace std;
int main(){
    int a;
    float q;
    cin>>a;
    if(a==1){
    	q=a*5.0;
	}
    else if(2<=a && a<=5){
    	q=a*4.5;
	}
    else if(6<=a && a<=10){
    	q=a*4.0;
	}
    else {
    	q=a*3.5;
	}
	printf("%.1f",q);
}
/**************************************************************
	Problem: 1717
	User: xiaojingxuan
	Language: C++
	Result: Accepted
	Time:51 ms
	Memory:2072 kb
****************************************************************/