#include <iostream>
#include <algorithm>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <numeric>
#include <bitset>
#include <cmath>
#include <limits>
#include <array>

static const int MOD = 998244353;
using ll = long long;
using uint = unsigned;
using ull = unsigned long long;
using namespace std;

template<class T> constexpr T INF = ::numeric_limits<T>::max() / 32 * 15 + 208;

void f(string &a, int &c, int n, int used){
    if(c <= 0) return;
    if(a.size() == n){
        if(used != 7) return;
        c--;
        if(c == 0){
            cout << a << endl;
        }
        return;
    }
    for (int i = 0; i < 3; ++i) {
        a += char('A' + i);
        f(a, c, n, used | (1 << i));
        if(c <= 0) return;
        a.pop_back();
    }
}

int main() {
    int n, c;
    cin >> n >> c;
    string a;
    f(a, c, n, 0);
    if(c > 0){
        cout << -1 << endl;
    }
    return 0;
}