using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine($"'{Preview("The lazy fox jumped over .. nah you know the drill", 15)}'");

        Console.WriteLine($"'{Preview("Thelazyfoxjumpedover..nahyouknowthedrill", 15)}'");

    }

    public static string Preview(ReadOnlySpan<char> input, int previewLength)

    {

        var trimmed = input[..previewLength];

        var ws = trimmed.LastIndexOf(' ');

        if (ws > 0) trimmed = trimmed[..ws];

        return trimmed.ToString();

    }

}