using System;
class Sample {
public static void Main() {
string str = "this is a test.";
int start;
int at;
string target = "is";
char[] anyOf = target.ToCharArray();
start = str.Length-1;
at = str.LastIndexOfAny(anyOf);
if (at > -1)
Console.Write(at);
else
Console.Write("(not found)");
Console.Write("{0}{0}{0}", Environment.NewLine);
}
}