String algorithm - GemStones - using one array instead of jagged array

GemStones2.cs

using System;

namespace Solution
{
    class Solution
    {
        static void Main(string[] args)
        {
            long numberOfCases = Convert.ToInt64(Console.ReadLine());
            string alphabet = "abcdefghijklmnopqrstuvwxyz";
            long[] gemOccurence = new long[alphabet.Length];
            string currentGem;
            long gemStones = 0;
            
            for(long currentCase = 0; currentCase < numberOfCases; currentCase++)
            {
                currentGem = Console.ReadLine();
                
                for(int currentAlphaChar = 0; currentAlphaChar < alphabet.Length; currentAlphaChar++)
                {
                    for(int currentGemChar = 0; currentGemChar < currentGem.Length; currentGemChar++)
                    {
                        if(currentGem[currentGemChar] == alphabet[currentAlphaChar])
                        {
                            gemOccurence[currentAlphaChar]++;
                            break;
                        }
                    }
                }
            }
            
            foreach(long number in gemOccurence)
            {
                if(number == numberOfCases)
                {
                    gemStones++;
                }
            }
            Console.WriteLine(gemStones);
        }
    }
}