#include<bits/stdc++.h>
using namespace std;
int main(){
    int a;
    float p;
    scanf("%d",&a);
    if (a>10){
        p=(a-10)*1.5+2.5;
        printf("%.2f",p);
    }
    else {
        p=2.5;
        printf("%.2f",p);
    }
    return 0;
}
/**************************************************************
	Problem: 1043
	User: xiaojingxuan
	Language: C++
	Result: Accepted
	Time:15 ms
	Memory:2076 kb
****************************************************************/