#include <bits/stdc++.h>
using namespace std;
int main(){
    int a;
    cin>>a;
    if(a<=10)
    printf("%.2f",2.5);
    else printf("%.2f",(a-10)*1.5+2.5);
}
/**************************************************************
	Problem: 1043
	User: chenmingyu
	Language: C
	Result: Compile Error
****************************************************************/