Format格式化的问题

using System;
public class format



{
public static void Main()
{
decimal x = 11111111.976m;
decimal y = 123456789123456789m;
Console.Write("Result is:");
Console.WriteLine(decimal.Format(x,"C"));
Console.Write("Result is:");
Console.WriteLine(decimal.Format(y,"C"));
}
}
错误提示：decimal并不包含对Format的定义，