#include <stdio.h>
int main(){
    int a;
    scanf("%d",&a);
    
   float q;
    if(a <= 10){
    	q = 2.5;
    }else{
    	q = 2.5 + (a-10) * 1.5;
    }
    
    printf("%.2f",q);
    return 0;
}
/**************************************************************
	Problem: 1043
	User: admin
	Language: C
	Result: Accepted
	Time:18 ms
	Memory:1144 kb
****************************************************************/