#include<iostream>
using namespace std;
int main()
{
int with;
double bal;
cin>>with>>bal;
if(with<bal)
{
if((with%5)==0)
{
bal=bal-with;
bal=bal-0.50;
printf("%.2f",bal);
}
else
printf("%.2f",bal);
}
else
printf("%.2f",bal);
}
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