public static void Main()
string s1 = "abcnhrkfldnndfjur";
int IndexOfA = s1.IndexOf(ch1);
int IndexOfB = s1.IndexOf(ch2);
int IndexOfC = s1.IndexOf(ch3);
if(IndexOfA == 0 && IndexOfB == 1 && IndexOfC == 2)
s1 = s1.Replace("abc", "www");
s1 = s1.Insert(s1.Length, s2);