#include <iostream>
#include <math.h>



using namespace std;

  void   licz ( double a, double b, double c = 5.0 )
{
  if (a <= b + 0.5){
    if ( fmod (a,c) == 0){
        cout << fixed  << b - a - 0.50;
    }
  }
   else { cout << fixed << b;}
}



int main( double a = 0, double b = 0)
{
cout.precision(2);
cin >> a >> b ;

 licz(a,b);

    return 0;
}