public class Solution {
    public int StrStr(string haystack, string needle) {
        for (int i = 0; i <= haystack.Length - needle.Length; i++)
        {
            bool matches = true;
            for (int j = 0; j < needle.Length; j++)
            {
                if (haystack[i + j] != needle[j])
                {
                    matches = false;
                    break;
                }
            }
            if (matches)
            {
                return i;
            }
        }
        return -1;
    }
}