#include <vector>
#include <iostream>
#include <string>
using namespace std;


double totalFunc(vector<double> l);

int main()
{
	double n, k, t = 0;
	string alpha = "abcdefghijklmnopqrst";
	while (true)
	{
		cin >> n >> k;
		string result = "";
		if (n == 0 && k == 0) break;
		vector<double> letters;
		t = 0;
		for (int i = 0; i < n; i++) {
			double j;
			cin >> j;
			t += j;
			letters.push_back(j);
		}
		// MAIN PROGRAM
		for (int i = 0; i < t; i++)
		{
			for (int j = 0; j < n; j++)
			{
				if (letters[j] > 0) {
					letters[j]--;
					double total = totalFunc(letters);
					if (k < total)
					{
						result += alpha[j];
						break;
					} else {
						k = k - total;
						letters[j]++;
					}
				}
			}
		}

		cout << result << endl;
	}

	return 0;
}

int UCLN(int a, int b) {
   while ((a != 0) && (b != 0)) {
      a = a%b;
      if (a != 0)
         b = b%a;
   }
   return a+b;
}

double totalFunc(vector<double> l)
{
	double n = l.size();
	double bigt = 0;
	vector<double> tarray;
	for(int i=0; i < n; i++)
	{
		bigt += l[i];
	}
	tarray.push_back(0);
	for(int i=1; i <=  bigt; i++)
	{
		tarray.push_back(i);
	}

	for(int i=0; i < n; i++)
	{
		for(int j=1; j <= l[i]; j++)
		{
         double jj = j;
			for(int k=1; k <= bigt; k++)
			{
            double x = UCLN(tarray[k], jj);
				if (x != 1)
				{
					tarray[k] = tarray[k] / x;
               jj = jj / x;
				}
				if (jj == 1) break;
			}
		}
	}
	double result = 1;
	for (int i = 1; i < tarray.size(); i++)
      result *= tarray[i];
	return result;
}