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

typedef long long LL;

LL n;
LL k;
LL akt;
LL newN = 1;

char small,big;

void inline switchLetters(char x) {
	if(x=='a') {
		small = 'b';
		big = 'c';
	} else if (x=='b') {
		small = 'a';
		big = 'c';
	} else {
		small = 'a';
		big = 'b';
	}
}

void go2() {
	while(k>1 && akt > 0) {
		//printf("\n%c%c-> k: %lld, akt: %lld\n",small,big,k,akt);
		k-=1;
		if(k<=akt-1) {
			//printf("%c",small);
			putchar(small);
			switchLetters(small);
		} else {
			k-=akt-1;
			//printf("%c", big);
			putchar(big);
			switchLetters(big);
		}
		akt/=2;
	}
}


void go() {
	//printf("N:%lld newN:%lld\n",n,newN); 
	//ile literek można wypisać na pałę?
	LL x = 0;
	LL calc = 2;
	while(calc-1<k-(n-x)){
		calc*=2;
		x++;
	}
	//printf("Na pale: %lld, x: %lld, n: %lld\n",n-x,x,n);
	int op = 1;
	bool byl = false;
	if(x<n) {
		while(n>x && k>1) {
			byl = true;
			if(op) {
				//printf("a");
				putchar('a');
				op=0;
			}
			else {
				//printf("b");
				putchar('b');
				op=1;
			}
			n--;
			k--;
		}
		//printf("\nKONIEC n: %lld\n\n",n);
	}
	akt = 1;
	while(n--) {
		akt*=2;
	}
	if(byl) {
		k++;
		if(op) {
			small = 'a';
			big = 'c';
		} else {
			small = 'b';
			big = 'c';
		}
		go2();
		printf("\n");
		//printf("\nKONIEC\n");
		return;
	}
	//printf("AKT %lld\n", akt);
	//printf("K:  %lld TEST:%lld\n", k, 3*(akt-1));
	if (k<=akt-1) {
		//printf("a");
		putchar('a');
		small = 'b';
		big = 'c';
		akt/=2;
		go2();
	} else {
		k-=akt-1;
		if(k<=akt-1) {
			//printf("b");
			putchar('b');
			small = 'a';
			big = 'c';
			akt/=2;
			go2();
		} else {
			k-=akt-1;
			//printf("c");
			putchar('c');
			small = 'a';
			big = 'b';
			akt/=2;
			go2();
		}
	}
	printf("\n");
}

int main(){
	scanf("%lld %lld",&n,&k);
	//recalc n
	newN = 0;
	LL calc = 1;
	while (3*(calc-1)<k) {
		calc*=2;
		newN++;
		//printf("%lld\n", calc);
	}
	//printf("newN: %lld, n: %lld, calc: %lld, k: %lld\n",newN,n,calc,k);
	if(n<newN) {
		printf("NIE\n");
	} else {
		go();
	}
	return 0;
}