using System;

using System.Text.RegularExpressions;

​

public class Program

{

    public static void Main()

    {

        string input = "Savings Account Account number ending in 6501 ****6501";

​

        // Pattern to match 'Account number ending in ' followed by digits and ' ****' followed by digits

        string pattern = @"Account number ending in \d{4} (\*\*\*\*\d{4})";

​

        // Use Regex.Replace to substitute the matched pattern with the masked account number part

        string output = Regex.Replace(input, pattern, "$1");

​

        Console.WriteLine(output); // Should print: 'Savings Account ****6501'

    }

}