using System;
using System.Linq;
using System.Collections.Generic;
 
class Program
{
    static void Main()
    {
        List<string> A = new List<string> { "123A", "456B", "789C", "ABCDE", "LONGSTRING", "XYZ", "AAZ" };
 
        var result = A.Select(s => s.First()) // Берем первый символ каждой строки
                      .Reverse() // Инвертируем порядок
                      .ToList();
 
        Console.WriteLine(string.Join(", ", result));
    }
}

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