#include <bits/stdc++.h>

using namespace std;

int main() {
    int N, S;
    cin >> N >> S;
    vector<vector<int>> ans;
    vector<int> A(N);
    auto dfs = [&] (auto dfs, int now) -> void {
        if (now == N) {
            bool ok = true;
            for (int i = 0; i <= 2; i++) {
                ok &= find(A.begin(), A.end(), i) != A.end();
            }
            if (ok) ans.push_back(A);
        } else {
            for (int i = 0; i <= 2; i++) {
                A[now] = i;
                dfs(dfs, now + 1);
            }
        }
    };
    dfs(dfs, 0);
    S--;
    if (S < ans.size()) {
        for (int i: ans[S]) cout << (char)('A' + i);
        cout << endl;
    } else {
        cout << -1 << endl;
    }
    return 0;
}