using System;

public class Hello
{
    static void Main()
    {
        string[] line = Console.ReadLine().Trim().Split(' ');
        var c = int.Parse(line[0]);
        var y = int.Parse(line[1]);
        getAns(c, y);
    }
    static int[] getArray(int y, int[] t)
    {
        var a = new int[6];
        for (int i = 0; i < 6; i++)
        {
            a[i] = y / t[i];
            y -= a[i] * t[i];
        }
        Array.Reverse(a);
        return a;
    }
    static void getAns(int c, int y)
    {
        var t = new int[] { 10000, 5000, 2000, 1000, 500, 100 };
        if (c * 100 > y) { Console.WriteLine("can't exchange"); return; }
        var a = getArray(y, t);
        if (a[0] + a[1] >= c) { Console.WriteLine("no exchange"); return; }
        c -= a[0];
        Console.WriteLine((c + 4) / 5 * 5);
    }
}