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#include <cstdio>
using namespace std;

int main()
{
    int n;
    long long k;
    scanf("%d %lld", &n, &k);

    long long slow = 3 * ((1 << n) - 1);
    if (slow < k) {
        printf("NIE\n");
    } else {
        char last = 'a';
        slow /= 3;
        while (k > slow) {
            ++last;
            k -= slow;
        }
        ++slow; // slow = 2 ^ n
        printf("%c", last);
        char available[4];
        while (k > 1) {
            --k;
            --slow;
            slow /= 2;
            available[0] = 'a';
            available[1] = 'b';
            available[2] = 'c';
            available[last - 'a'] = '\0';
            for (int i = 0; i < 3; ++i)
                if (available[i] == '\0') {
                    available[i] = available[i+1];
                    available[i+1] = '\0';
                }
            last = available[0];
            if (slow < k) {
                k -= slow;
                last = available[1];
            }
            printf("%c", last);
        }
        printf("\n");
    }

    return 0;
}