include<iostream>

include<iomanip>

include<math.h>

using namespace std; bool check(int x) { if(x%5==0) return true; else return false; }

float withdraw(float balance, int amt) { return (balance-amt-.50); }

int main() { int amount; float balance;

cin>>amount>>balance;

cout.setf(ios::fixed);

if(amount>0 && amount <= 2000 && balance>0 && balance<=2000)
{
   if(balance>=amount)
   {
     if(check(amount))
     {

        cout<<setprecision(2)<<withdraw(balance,amount);
     }
     else
     cout<<setprecision(2)<< balance;
    }
     else
     cout<<setprecision(2)<<balance;
 }


return 0;

}