#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using ll = long long;
using ull = unsigned long long;
using mint = atcoder::modint998244353;
using maxt = atcoder::modint1000000007;
//ここからグラフ探索系
using Graph = vector<vector<int>>;
struct edge {
  int to;
  ll cost;
};
edge make_edge(int a, ll b) {
  edge ans;
  ans.to = a, ans.cost = b;
  return ans;
}
using Cost_Graph = vector<vector<edge>>;
using D_heap = priority_queue<pair<ll, int>, vector<pair<ll, int>>, greater<pair<ll, int>>>;
vector<int> bfs_01(Cost_Graph G, int s) {//01_BFS
  vector<int> ans(G.size() + 1, -1);
  deque<pair<int, int>> que;
  que.push_back(make_pair(0, s));
  while(!que.empty()) {
    auto v = que.front();
    que.pop_front();
    if(ans[v.second] != -1) {
      continue;
    }
    ans[v.second] = v.first;
    for(edge next_v : G[v.second]) {
      if(ans[next_v.to] != -1) {
        continue;
      }
      if(next_v.cost) {
        que.push_back(make_pair(v.first + 1, next_v.to));
      }
      else {
        que.push_front(make_pair(v.first, next_v.to));
      }
    }
  }
  return ans;
}
vector<ll> dijkstra(Cost_Graph G, int s) {//ダイクストラ法
  vector<ll> ans(G.size() + 1, -1);
  D_heap que;
  que.push(make_pair(0, s));
  while(!que.empty()) {
    auto v = que.top();
    que.pop();
    if(ans[v.second] != -1) {
      continue;
    }
    ans[v.second] = v.first;
    for(edge next_v : G[v.second]) {
      if(ans[next_v.to] != -1) {
        continue;
      }
      que.push(make_pair(v.first + next_v.cost, next_v.to));
    }
  }
  return ans;
}
//グラフ探索系終わり
vector<ll> Era(int N) {
  vector<ll> ans(0, 0);
  vector<bool> isprime(N + 1, true);
  isprime[1] = false;
  for(int i = 1; i <= N; i++) {
    if(isprime[i]) {
      ans.push_back(i);
      for(int j = 2 * i; j <= N; j += i) {
        isprime[j] = false;
      }
    }
  }
  return ans;
}
ll POW(ll a, ll N) {
  if(N == 0) {
    return 1;
  }
  ll tmp = POW(a, N / 2), ans = tmp * tmp;
  if(N % 2 == 1) {
    ans *= a;
  }
  return ans;
}
ll GCD(ll a, ll b) {
  if(b == 0) {
    return a;
  }
  ll r = a % b;
  return GCD(b, r);
}
ll LCM(ll a, ll b) {
  return (a * b) / GCD(a, b);
}
vector<ll> zaatu(vector<ll> a) {
  vector<ll> b(0, 0);
  b = a;
  sort(b.begin(), b.end());
  b.erase(unique(b.begin(), b.end()), b.end());
  int s = b.size();
  for(ll &o : a) {
    int l = 0, r = s, c = 0;
    while(r - l > 1) {
      c = (l + r) / 2;
      if(b.at(c) <= o) {
        l = c;
      }
      else {
        r = c;
      }
    }
    o = r;
  }
  return a;
}
struct FenwickTree {
  int N;
  vector<ll> a;
  
  FenwickTree(int n) {
    N = n;
    a.assign(N + 1, 0);
  }
  
  void add(int i, ll x) {
    for(int j = i; j <= N; j += (j & -j)) {
      a[j] += x;
    }
  }
  
  ll sum(int i, int j) {
    return sum_sub(j) - sum_sub(i - 1);
  }
  
  ll sum_sub(int i) {
    if(i == 0) {
      return 0;
    }
    ll s = 0;
    for(int j = i; j > 0; j -= (j & -j)) {
      s += a[j];
    }
    return s;
  }
};
ll tento(vector<ll> a) {
  int s = a.size();
  FenwickTree tmp(s);
  ll ans = 0;
  for(int i = 0; i < s; i++) {
    ans += i - tmp.sum_sub(a.at(i));
    tmp.add(a.at(i), 1);
  }
  return ans;
}
ll solve_qe(ll a, ll b, ll c) {
  ll l = 0, r = (ll)1e9 + 1, mid = 0;
  while(r - l > 1) {
    mid = (l + r) / 2;
    if(a * POW(mid, 2) + b * mid + c <= 0) {
      l = mid;
    }
    else {
      r = mid;
    }
  }
  if(a * POW(l, 2) + b * l + c == 0) {
    return l;
  }
  return -1;
}
vector<int> Manacher(string S) {
  int i = 0, j = 0, s = S.size();
  vector<int> ans(s, 0);
  while(i < s) {
    while(i >= j && i + j < s && S[i - j] == S[i + j]) {
      j++;
    }
    ans[i] = j;
    int k = 1;
    while(i >= k && k + ans[i - k] < j) {
      ans[i + k] = ans[i - k], k++;
    }
    i += k, j -= k;
  }
  return ans;
}
//メモ
//__builtin_popcount
//next_permutation
//srand((unsigned)time(NULL))
//cout << fixed << setprecision(Digit);
//A～Z=65～90,a～z=97～122,0～9=48～57
//メモ終わり
//library end

int main() {
	int N;
	cin >> N;
	vector<string> W;
	vector<int> cnt(3, 0);
	for(int i = 0; i < POW(3, N); i++) {
		string tmp;
		for(int j = 0; j < N; j++) {
			tmp += (char)(i / POW(3, j) % 3 + 65);
		}
		cnt.assign(3, 0);
		for(int j = 0; j < N; j++) {
			cnt[tmp[j] - 'A']++;
		}
		int f = 1;
		for(int o : cnt) {
			f = (o ? f : 0);
		}
		if(f) {
			W.push_back(tmp);
		}
	}
	sort(W.begin(), W.end());
	int S;
	cin >> S;
	cout << (S > (int)W.size() ? "-1" : W[S - 1]) << endl;
}