#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for (int i = 0; i< (n); ++i)
#define repi(i, a, b) for (int i = (a); i < (b); ++i)
#define all(x) (x).begin(), (x).end()
#define fore(i, a) for(auto &i:a)
using ll = long long;

int main() {
  int n;cin >> n;
	int s;cin >> s;
	vector<int> three(n+2), two(n+2);
	three[0] = 1;two[0] = 1;
	rep(i, n+1){
		three[i+1] = three[i]*3;
		two[i+1] = two[i]*2;
	}
	int rem = s;
	bool eA = false,eB = false, eC = false;
	string ans(n, '*');
	vector<char> clist ={'A','B','C'};
	rep(i, n){
		fore(c, clist){
			int t = (eA || c == 'A')+(eB || c == 'B')+(eC || c == 'C');
			int kouho;
			if(t == 1){
				kouho = three[n-1-i]-two[n-i]+1;
			}
			else if(t == 2){
				kouho = three[n-1-i]-two[n-1-i];
			}
			else{
				kouho = three[n-1-i];
			}
			if(rem > kouho){
				rem-=kouho;
				if(c == 'C'){
					cout << -1 << endl;
					return 0;
				}
			}
			else{
				ans[i] = c;
				if(c == 'A')eA = true;
				if(c == 'B')eB = true;
				if(c == 'C')eC = true;
				break;
			}
		}
	}
	if(rem == 1){
		cout << ans << endl;
	}
	else{
		cout << -1 << endl;
	}

}