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//Krzysztof Pieprzak
#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef long double ld;
typedef unsigned long long ull;
typedef unsigned int uint;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef pair<int,int> pii;
typedef pair<long long, long long> pll;
typedef vector<pii> vpii;
typedef vector<pll> vpll;

#define Size(x) (int)x.size()
#define VAR(v,n) auto v = (n)
#define FOR(i,a,b) for(VAR(i,a); i < (b); ++i)
#define FORE(i,a,b) for(VAR(i,a); i <= (b); ++i)
#define FORREV(i,a,b) for(VAR(i,b); i >= (a); --i)
#define FORSTEP(i,a,b,step) for(VAR(i,a); i < (b); i += (step))
#define FOREACH(i,c) for(auto i : (c))
#define FOREACHS(i,c,n) for(VAR(i,&(c)[0]); i-(c)<(n); ++i)
#define ALL(x) x.begin(),x.end()
#define CLEAR(t) memset(t, 0, sizeof(t))
#define F first
#define S second
#define MP make_pair
#define PUB push_back
#define POB pop_back
#define pieprzu ios_base::sync_with_stdio(0);

const int    INF = 1000000001;
const double EPS = 10e-9;

const int MAXN = 1000000;
const int LETTERS = 3;
const ll MAXK = 1000000000000000000LL;
const int MAXK_LOG = 60;

ll myPow[MAXK_LOG+10];
char word[MAXN+10];

void initPow() {
    myPow[0] = 1;
    FORE (i, 1, MAXK_LOG) {
        myPow[i] = myPow[i-1]*2;
    }
}

inline ll getWordsFixFirstLetter(int len) {
    return myPow[len] - 1;
}

inline ll getWords(int len) {
    return getWordsFixFirstLetter(len) * LETTERS;
}

bool check(int n, ll k) {
    if (n > 60) {
        return true;
    }

    return k <= getWords(n);
}

void createWord(int n, ll k) {
    int forbiddenLetter = -1;
    int pos = 0;
    while (k > 0) {
        if (n > MAXK_LOG) {
            word[pos] = forbiddenLetter == 0 ? 'b' : 'a';
            --k;
        } else {
            ll sum = 0;
            FOR (letter, 0, LETTERS) {
                if (letter != forbiddenLetter) {
                    if (k <= sum + getWordsFixFirstLetter(n)) {
                        word[pos] = 'a' + letter;
                        k -= sum+1;
                        break;
                    }

                    sum += getWordsFixFirstLetter(n);
                }
            }
        }

        forbiddenLetter = word[pos]-'a';
        ++pos;
        --n;
    }
}

void rob(int test) {
    int n;
    ll k;
    scanf("%d %lld", &n, &k);

    initPow();
    if (!check(n, k)) {
        printf("NIE\n");
        return;
    }

    createWord(n, k);
    printf("%s\n", word);
}

int main() {
    int test = 1;
    //scanf("%d", &test);

    FORE (i, 1, test) rob(i);

    return 0;
}