#include <bits/stdc++.h>
using namespace std;

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

    int a = 0,b = 0,c = 0,N,S; cin >> N >> S;
    string now = "",answer = "";
    auto dfs = [&](auto dfs) -> void {
        if(now.size() == N){
            if(min({a,b,c}) > 0){
                S--;
                if(S == 0) answer = now;
            }
            return;
        }
        now += 'A'; a++;
        dfs(dfs);
        now.pop_back(); a--;
        now += 'B'; b++;
        dfs(dfs);
        now.pop_back(); b--;
        now += 'C'; c++;
        dfs(dfs);
        now.pop_back(); c--;
    };
    dfs(dfs);
    if(answer == "") answer = "-1";
    cout << answer << endl;
}