#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)

void solve() {
  ll n, s;
  cin >> n >> s;
  vector<ll> c(3, 0), now;
  auto dfs = [&](auto self) -> void {
    if (s <= 0)
      return;
    if (ll(now.size()) == n) {
      bool ok = true;
      rep(i, 3) ok &= c[i] > 0;
      if (ok) {
        s--;
        if (s == 0) {
          rep(i, n) cout << char('A' + now[i]);
          cout << '\n';
        }
      }
      return;
    }
    rep(i, 3) {
      now.push_back(i);
      c[i]++;
      self(self);
      c[i]--;
      now.pop_back();
    }
  };
  dfs(dfs);
  if (s > 0)
    cout << "-1\n";
}

int main() {
  std::cin.tie(nullptr);
  std::ios_base::sync_with_stdio(false);
  int T = 1;
  for (int t = 0; t < T; t++) {
    solve();
  }
  return 0;
}