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#include <cstdio>
#define P(x) (1ll<<(x))
using namespace std;
typedef long long LL;

const char C[3][2] = {{'b', 'c'}, {'a', 'c'}, {'a', 'b'}};

LL n, k;


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

  if (n <= 60 && k+3 > 3*P(n)) {
    puts("NIE");
  } else {
    int div = P(n)-1;
    char c = 'a' + (k+div-1)/div - 1;
    putchar(c);

    k = (k-1)%div+1;
    bool start = false;
    for (LL i=P(60); i; i>>=1) {
      // printf("\n%lld\n", LL(k));
      if (start) {
        c = C[c-'a'][bool(k&i)];
        putchar(c);
      } else start = k&i;
    }
    putchar('\n');
  }
  return 0;
}