import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
 
class atm {
 
    public static void main(String[] args) throws Exception {
        BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
        String[] inp=br.readLine().split(" ");;
        double x=Double.parseDouble(inp[0]);
        double y=Double.parseDouble(inp[1]);
 
        if((x<y+0.5)&&(x%5==0))
            y=y-x-0.5;
 
            System.out.printf("%.2f\n",y);
        }
    }
 

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NDIgMTIwLjAw

42 120.00