using System.Text.RegularExpressions;
using System;

public class Test
{
	public static void Main()
	{
		String s = "0787654321";
       if (!Regex.IsMatch(s, @"^078\d{7}")) {
       Console.WriteLine("Error! Wrong format.");
}
      else {
      Console.WriteLine("Correct format.");
      }
      }
	
}