using System;
using System.Linq;

public class Test
{
	public static void Main()
	{
byte[] large = new byte[100];
for (byte i = 0; i < 100; i++) {
    large[i] = i;
}
byte[] small = new byte[] { 23, 24, 25 };
var res = Enumerable
    .Range(0, large.Length-1)
    .Cast<int?>()
    .FirstOrDefault(n => large.Skip(n.Value).Take(small.Length).SequenceEqual(small));
Console.WriteLine(res);
	}
}