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#include <cstdio>
#include <iostream>
using namespace std;

typedef long long LL;

#define REP(i,n) for (LL i = 0; i < n; ++i)
#define FOR(i,a,b) for (LL i = a; i <= b; ++i)

//#define DEBUG

// x = dlog(n)
// 2^(x-1) <= n <= 2^x - 1

LL dlog(LL n) {
    LL r = 0;
    while (n > 0) {
        r++;
        n /= 2;
    }
    return r;
}

LL pwr(LL n) {
    if (n == 0)
        return 1;
    else if (n % 2 == 1) {
        return 2 * pwr(n-1);
    }
    else {
        LL tmp = pwr(n/2);
        return tmp * tmp;
    }
}

char smaller (char x) {
    return (x == 'a') ? 'b' : 'a';
}

char bigger (char x) {
    return (x == 'c') ? 'b' : 'c';
}

// a <= 2^b
bool mniejsze(LL a, LL b) {
    return dlog(a-1) <= b;
}

void fun(LL n, LL k) {
    LL d = dlog(k);
    LL d2 = dlog((k+1)/2);
    LL d3 = dlog((k+2)/3);
    LL x = k;
    char last = ' ';

#ifdef DEBUG
    printf("\nd = %lld, d2 = %lld, d3 = %lld\n", d, d2, d3);
#endif

    if (d <= n) {
        printf("a");
        x = k - 1;
        last = 'a';
    }
    else if (d2 <= n) {
        printf("b");
        x = k - 1 - (pwr(n) - 1);
        last = 'b';
    }
    else if (d3 <= n) {
        printf("c");
        x = k - 1 - 2 * (pwr(n) - 1);
        last = 'c';
    }
    else {
        printf("NIE\n");
        return;
    }
   
    LL krok = 1;
    while (x > 0) {
#ifdef DEBUG
        printf("dd = %lld\n", d);
#endif
        if (mniejsze(x+1, n - krok)) {
            char next = smaller(last);
            printf("%c", next);
            last = next;
            x--;
        }
        else {
            char next = bigger(last);
            printf("%c", next);
            last = next;
            x = x - 1 - (pwr(n-krok) - 1);
        }
        krok++;

    }
    printf("\n");
}

int main() {
    LL n, k;

#ifdef DEBUG
    FOR(k,1,50) {
        //printf("%lld %lld\n", k, dlog(k));
        printf("%lld ", k);
        fun(4, k); 
    }

#endif
#ifndef DEBUG
    scanf("%lld %lld", &n, &k);

    fun(n, k);
#endif
    return 0;
}