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#include <iostream>
#include <vector>

using namespace std;

typedef unsigned long long ll;

const ll INF = 5000000000000000000;

int main()
{
    ios_base::sync_with_stdio(0);
    ll n, k;
    cin >> n >> k;
    vector<ll> pot(n + 1, INF), sumy(n + 1, INF);
    pot[0] = 1;
    sumy[0] = 1;
    for (int i = 1; i < n + 1; ++i)
    {
        pot[i] = pot[i - 1] * 2LL;
        sumy[i] = sumy[i - 1] + pot[i];
        if (sumy[i] > INF)
        {
            sumy[i] = INF;
            break;
        }
    }
    string odp = "";
    for (int i = 1; i <= n; ++i)
    {
        if (k == 1 && i > 1) break;
        if (i > 1) --k;
        if (i == 1 || (i > 1 && odp[i - 2] != 'a'))
        {
            if (sumy[n - i] >= k)
            {
                odp += "a";
                continue;
            }
            else k -= sumy[n - i];
        }
        if (i == 1 || (i > 1 && odp[i - 2] != 'b'))
        {
            if (sumy[n - i] >= k)
            {
                odp += "b";
                continue;
            }
            else k -= sumy[n - i];
        }
        if (i == 1 || (i > 1 && odp[i - 2] != 'c'))
        {
            if (sumy[n - i] >= k)
            {
                odp += "c";
                continue;
            }
            else k -= sumy[n - i];
        }
        if (odp == "")
        {
            cout << "NIE";
            return 0;
        }
    }
    cout << odp;
    return 0;
}