public static void Main()
for (double a = min; a <= max; a++)
for (double b = min; b <= max; b++)
for (double c = min; c <= max; c++)
for (double d = min; d <= max; d++)
if(a + b + c == 100 && a + 10 * b + 50 * c == 500)
Console.WriteLine("a=" + a + ", b=" + b + ", c=" + c + ", d=" + d);