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

#include <atcoder/all>
using namespace atcoder;

using ll = long long;
using mint = modint998244353;

int main() {
  int N;
  cin >> N;
  string S(N, '*');
  vector<string> v;
  auto dfs = [&](auto dfs, int i) -> void {
    if(i == N) {
      int f = 0;
      for(char c : S) f |= 1 << (c - 'A');
      if(f == 7) v.push_back(S);
    }else {
      for(char c : "ABC") {
        S[i] = c;
        dfs(dfs, i + 1);
      }
    }
  };
  dfs(dfs, 0);
  int p;
  cin >> p;
  cout << (p <= (int)v.size() ? v[p - 1] : "-1") << endl;
}