#include<stdio.h>
#include<stdlib.h>
int main()
{	float n,s;
	scanf("%f",&s);
	if(s<=15)
	{	
		n=s/1.5;
		printf("%.2f",n);
	}
	if(s>15)
	{
		n=(s-15)/2.5+10;
	printf("%.2f",n);
	}
}
	
/**************************************************************
	Problem: 1052
	User: admin
	Language: C
	Result: Accepted
	Time:8 ms
	Memory:1144 kb
****************************************************************/