#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define all(x) (x).begin(), (x).end()
using ll = long long;
const ll MOD = 998244353;


int main() {
    int n,s;
    cin >> n >> s;
    vector<char> abc={'A','B','C'};
    vector<vector<char>> ans;
    function<void(vector<char>)> dp=[&](vector<char> S){
        if (S.size() == n) {
            if (count(all(S), abc.at(0)) && count(all(S), abc.at(1)) && count(all(S), abc.at(2))) {
                ans.push_back(S);
            } 
        }
        else {
            for (char c : abc) {
                S.push_back(c);
                dp(S);
                S.pop_back();
            }
        }
    };
    dp({});
    sort(all(ans));
    if (s > ans.size()) {
        cout << -1 << endl;
        return 0;
    }
    for (auto s : ans.at(s-1)){
        cout << s;
    }
    cout << endl;

}