Find match string between 2 String

static string FindMatchString()
       {
           string string1 = "TodayisSaturday";
           string string2 = "HowisSaturday";

           string smallString = string1.Length > string2.Length ? string2 : string1;
           string bigString = string1.Length > string2.Length ? string1 : string2;

           string resultString = "";

           int smallStringLen = smallString.Length;
           int bigStringLen = bigString.Length;

           for (int i = smallStringLen - 1; i >= 0; i--)
           {

               if (smallString[i] == bigString[bigStringLen - 1])
               {
                   resultString = resultString + smallString[i].ToString();
               }
               bigStringLen--;
           }

           char[] arr = resultString.ToCharArray();

           Array.Reverse(arr);
           return new string(arr);


       }