Removing duplicates from two strings

char[] delimiterChars = { ',' };

string a = "1,3,2,4,5";
string b = "3,4";

string[] A = a.Split(delimiterChars);
string[] B = b.Split(delimiterChars);

List<string> C = A.Except<string>(B).ToList();
string c = string.Join(",", C);

for (int i = 0; i < s1.Length; i++)
{
    int count = 0;
    if (s1[i] != ',')
    {

        for (int j = 0; j < s2.Length; j++)
        {
            if (s1[i].ToString() == s2[j].ToString())
            {
                count++;
            }
        }
        if (count == 0)
            s3 += s1[i].ToString() + ',';
    }
}
s3.Remove(s3.Length - 1);

string s1 = "1,2,3,4,5";
        string s2="2,3";
        var res1 = s1.Split(',');
        var res2 = s2.Split(',');
        string res = "";
        for(int i=0;i<res1.count();i++)>
        {
            for(int j=0;j<res2.count();>
            {
                if (res1[i] == res2[j])
                {
                    break;
                }
                else
                {
                    if ((j == (res2.Count() - 1)))
                    {

                        res = res + res1[i].ToString() + ",";
                    }
                }
            }
        }