using System;
using System.Linq;
using System.Collections.Generic;

namespace _5._PageCalculator
{
    class Program
    {
        static void Main(string[] args)
        {
            List<string> words = Console.ReadLine()
                .Split(new[] { ' ', ',' }, StringSplitOptions.RemoveEmptyEntries)
                .ToList();
            double wordsPerPage = double.Parse(Console.ReadLine());
            string keyword = Console.ReadLine();
            if (words.Contains(keyword))
            {
                int position = words.LastIndexOf(keyword);
                double output = Math.Ceiling(++position / wordsPerPage);
                Console.WriteLine(output);
            }
            else
            {
                Console.WriteLine("-1");
            }
        }
    }
}