#include <bits/stdc++.h>
#include <cassert>
using namespace std;
using ll = long long int;
using u64 = unsigned long long;
using pll = pair<ll, ll>;
// #include <atcoder/all>
// using namespace atcoder;
#define REP(i, a, b) for (ll i = (a); i < (b); i++)
#define REPrev(i, a, b) for (ll i = (a); i >= (b); i--)
#define ALL(coll) (coll).begin(), (coll).end()
#define SIZE(v) ((ll)((v).size()))
#define REPOUT(i, a, b, exp, sep) REP(i, (a), (b)) cout << (exp) << (i + 1 == (b) ? "" : (sep)); cout << "\n"

// @@ !! LIM(debug)

// ---- inserted function f:<< from util.cc

// declarations

template <typename T1, typename T2>
ostream& operator<< (ostream& os, const pair<T1,T2>& p);

template <typename T1, typename T2, typename T3>
ostream& operator<< (ostream& os, const tuple<T1,T2,T3>& t);

template <typename T1, typename T2, typename T3, typename T4>
ostream& operator<< (ostream& os, const tuple<T1,T2,T3,T4>& t);

template <typename T1, typename T2, typename T3, typename T4, typename T5>
ostream& operator<< (ostream& os, const tuple<T1,T2,T3,T4,T5>& t);

template <typename T1, typename T2, typename T3, typename T4, typename T5, typename T6>
ostream& operator<< (ostream& os, const tuple<T1,T2,T3,T4,T5,T6>& t);

template <typename T>
ostream& operator<< (ostream& os, const vector<T>& v);

template <typename T, typename C>
ostream& operator<< (ostream& os, const set<T, C>& v);

template <typename T, typename C>
ostream& operator<< (ostream& os, const unordered_set<T, C>& v);

template <typename T, typename C>
ostream& operator<< (ostream& os, const multiset<T, C>& v);

template <typename T1, typename T2, typename C>
ostream& operator<< (ostream& os, const map<T1, T2, C>& mp);

template <typename T1, typename T2, typename C>
ostream& operator<< (ostream& os, const unordered_map<T1, T2, C>& mp);

template <typename T, typename T2>
ostream& operator<< (ostream& os, const queue<T, T2>& orig);

template <typename T, typename T2>
ostream& operator<< (ostream& os, const deque<T, T2>& orig);

template <typename T, typename T2, typename T3>
ostream& operator<< (ostream& os, const priority_queue<T, T2, T3>& orig);

template <typename T>
ostream& operator<< (ostream& os, const stack<T>& st);

#if __cplusplus >= 201703L
template <typename T>
ostream& operator<< (ostream& os, const optional<T>& t);
#endif

ostream& operator<< (ostream& os, int8_t x);

ostream& operator<< (ostream& os, const __int128& x);

// definitions

template <typename T1, typename T2>
ostream& operator<< (ostream& os, const pair<T1,T2>& p) {
  os << "(" << p.first << ", " << p.second << ")";
  return os;
}

template <typename T1, typename T2, typename T3>
ostream& operator<< (ostream& os, const tuple<T1,T2,T3>& t) {
  os << "(" << get<0>(t) << ", " << get<1>(t)
     << ", " << get<2>(t) << ")";
  return os;
}

template <typename T1, typename T2, typename T3, typename T4>
ostream& operator<< (ostream& os, const tuple<T1,T2,T3,T4>& t) {
  os << "(" << get<0>(t) << ", " << get<1>(t)
     << ", " << get<2>(t) << ", " << get<3>(t) << ")";
  return os;
}

template <typename T1, typename T2, typename T3, typename T4, typename T5>
ostream& operator<< (ostream& os, const tuple<T1,T2,T3,T4,T5>& t) {
  os << "(" << get<0>(t) << ", " << get<1>(t)
     << ", " << get<2>(t) << ", " << get<3>(t) << ", " << get<4>(t) << ")";
  return os;
}

template <typename T1, typename T2, typename T3, typename T4, typename T5, typename T6>
ostream& operator<< (ostream& os, const tuple<T1,T2,T3,T4,T5,T6>& t) {
  os << "(" << get<0>(t) << ", " << get<1>(t)
     << ", " << get<2>(t) << ", " << get<3>(t) << ", " << get<4>(t) << ", " << get<5>(t) << ")";
  return os;
}

template <typename T>
ostream& operator<< (ostream& os, const vector<T>& v) {
  os << '[';
  for (auto it = v.begin(); it != v.end(); it++) {
    if (it != v.begin()) os << ", ";
    os << *it;
  }
  os << ']';

  return os;
}

template <typename T, typename C>
ostream& operator<< (ostream& os, const set<T, C>& v) {
  os << '{';
  for (auto it = v.begin(); it != v.end(); it++) {
    if (it != v.begin()) os << ", ";
    os << *it;
  }
  os << '}';

  return os;
}

template <typename T, typename C>
ostream& operator<< (ostream& os, const unordered_set<T, C>& v) {
  os << '{';
  for (auto it = v.begin(); it != v.end(); it++) {
    if (it != v.begin()) os << ", ";
    os << *it;
  }
  os << '}';

  return os;
}

template <typename T, typename C>
ostream& operator<< (ostream& os, const multiset<T, C>& v) {
  os << '{';
  for (auto it = v.begin(); it != v.end(); it++) {
    if (it != v.begin()) os << ", ";
    os << *it;
  }
  os << '}';

  return os;
}

template <typename T1, typename T2, typename C>
ostream& operator<< (ostream& os, const map<T1, T2, C>& mp) {
  os << '[';
  for (auto it = mp.begin(); it != mp.end(); it++) {
    if (it != mp.begin()) os << ", ";
    os << it->first << ": " << it->second;
  }
  os << ']';

  return os;
}

template <typename T1, typename T2, typename C>
ostream& operator<< (ostream& os, const unordered_map<T1, T2, C>& mp) {
  os << '[';
  for (auto it = mp.begin(); it != mp.end(); it++) {
    if (it != mp.begin()) os << ", ";
    os << it->first << ": " << it->second;
  }
  os << ']';

  return os;
}

template <typename T, typename T2>
ostream& operator<< (ostream& os, const queue<T, T2>& orig) {
  queue<T, T2> que(orig);
  bool first = true;
  os << '[';
  while (!que.empty()) {
    T x = que.front(); que.pop();
    if (!first) os << ", ";
    os << x;
    first = false;
  }
  return os << ']';
}

template <typename T, typename T2>
ostream& operator<< (ostream& os, const deque<T, T2>& orig) {
  deque<T, T2> que(orig);
  bool first = true;
  os << '[';
  while (!que.empty()) {
    T x = que.front(); que.pop_front();
    if (!first) os << ", ";
    os << x;
    first = false;
  }
  return os << ']';
}

template <typename T, typename T2, typename T3>
ostream& operator<< (ostream& os, const priority_queue<T, T2, T3>& orig) {
  priority_queue<T, T2, T3> pq(orig);
  bool first = true;
  os << '[';
  while (!pq.empty()) {
    T x = pq.top(); pq.pop();
    if (!first) os << ", ";
    os << x;
    first = false;
  }
  return os << ']';
}

template <typename T>
ostream& operator<< (ostream& os, const stack<T>& st) {
  stack<T> tmp(st);
  os << '[';
  bool first = true;
  while (!tmp.empty()) {
    T& t = tmp.top();
    if (first) first = false;
    else os << ", ";
    os << t;
    tmp.pop();
  }
  os << ']';
  return os;
}

#if __cplusplus >= 201703L
template <typename T>
ostream& operator<< (ostream& os, const optional<T>& t) {
  if (t.has_value()) os << "v(" << t.value() << ")";
  else               os << "nullopt";
  return os;
}
#endif

ostream& operator<< (ostream& os, int8_t x) {
  os << (int32_t)x;
  return os;
}

// for Enum type; just displays ordinals.
template <typename E>
typename std::enable_if<std::is_enum<E>::value, std::ostream&>::type
operator<<(std::ostream& os, E e) {
    return os << static_cast<typename std::underlying_type<E>::type>(e);
}

// This is a very ad-hoc implementation...
ostream& operator<<(ostream& os, const __int128& v) {
  unsigned __int128 a = v < 0 ? -v : v;
  ll i = 0;
  string s(64, ' ');
  if (v == 0) {
    s[i++] = '0';
  }else {
    while (a > 0) {
      s[i++] = '0' + (char)(a % 10);
      a /= 10;
    }
  }
  if (v < 0) {
    s[i++] = '-';
  }
  s.erase(s.begin() + i, s.end());
  reverse(s.begin(), s.end());
  os << s;
  return os;
}


// ---- end f:<<

// ---- inserted library file debug.cc
template <class... Args>
string dbgFormat(const char* fmt, Args... args) {
  size_t len = snprintf(nullptr, 0, fmt, args...);
  char buf[len + 1];
  snprintf(buf, len + 1, fmt, args...);
  return string(buf);
}

template <class Head>
void dbgLog(bool with_nl, Head&& head) {
  cerr << head;
  if (with_nl) cerr << endl;
}

template <class Head, class... Tail>
void dbgLog(bool with_nl, Head&& head, Tail&&... tail)
{
  cerr << head << " ";
  dbgLog(with_nl, forward<Tail>(tail)...);
}

#if DEBUG
  #define DLOG(...)        dbgLog(true, __VA_ARGS__)
  #define DLOGNNL(...)     dbgLog(false, __VA_ARGS__)
  #define DFMT(...)        cerr << dbgFormat(__VA_ARGS__) << endl
  #define DCALL(func, ...) func(__VA_ARGS__)
#else
  #define DLOG(...)
  #define DLOGNNL(...)
  #define DFMT(...)
  #define DCALL(func, ...)
#endif

/*
#if DEBUG_LIB
  #define DLOG_LIB(...)        dbgLog(true, __VA_ARGS__)
  #define DLOGNNL_LIB(...)     dbgLog(false, __VA_ARGS__)
  #define DFMT_LIB(...)        cerr << dbgFormat(__VA_ARGS__) << endl
  #define DCALL_LIB(func, ...) func(__VA_ARGS__)
#else
  #define DLOG_LIB(...)
  #define DFMT_LIB(...)
  #define DCALL_LIB(func, ...)
#endif
*/

#define DUP1(E1)       #E1 "=", E1
#define DUP2(E1,E2)    DUP1(E1), DUP1(E2)
#define DUP3(E1,...)   DUP1(E1), DUP2(__VA_ARGS__)
#define DUP4(E1,...)   DUP1(E1), DUP3(__VA_ARGS__)
#define DUP5(E1,...)   DUP1(E1), DUP4(__VA_ARGS__)
#define DUP6(E1,...)   DUP1(E1), DUP5(__VA_ARGS__)
#define DUP7(E1,...)   DUP1(E1), DUP6(__VA_ARGS__)
#define DUP8(E1,...)   DUP1(E1), DUP7(__VA_ARGS__)
#define DUP9(E1,...)   DUP1(E1), DUP8(__VA_ARGS__)
#define DUP10(E1,...)   DUP1(E1), DUP9(__VA_ARGS__)
#define DUP11(E1,...)   DUP1(E1), DUP10(__VA_ARGS__)
#define DUP12(E1,...)   DUP1(E1), DUP11(__VA_ARGS__)
#define GET_MACRO(_1,_2,_3,_4,_5,_6,_7,_8,_9,_10,_11,_12,NAME,...) NAME
#define DUP(...)          GET_MACRO(__VA_ARGS__, DUP12, DUP11, DUP10, DUP9, DUP8, DUP7, DUP6, DUP5, DUP4, DUP3, DUP2, DUP1)(__VA_ARGS__)
#define DLOGK(...)        DLOG(DUP(__VA_ARGS__))
#define DLOGKL(lab, ...)  DLOG(lab, DUP(__VA_ARGS__))

#if DEBUG_LIB
  #define DLOG_LIB   DLOG
  #define DLOGK_LIB  DLOGK
  #define DLOGKL_LIB DLOGKL
#endif

// ---- end debug.cc

// @@ !! LIM -- end mark --

int main(/* int argc, char *argv[] */) {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);
  cout << setprecision(20);

  vector<ll> power3(13);
  power3[0] = 1;
  REP(i, 1, 13) power3[i] = power3[i - 1] * 3;
  vector<ll> fact(4);
  fact[0] = 1; fact[1] = 1; fact[2] = 2; fact[3] = 6;

  vector tbl(8, vector(13, -1LL));
  auto f = [&](auto rF, u64 x, ll len) -> ll {
    ll& r = tbl[x][len];
    if (r < 0) {
      if (len == 0) {
        if (x == 0) r = 1;
        else r = 0;
      }
      else if (x == 0) r = power3[len];
      else if (popcount(x) > len) r = 0;
      else if (popcount(x) == len) r = fact[len];
      else {
        r = 0;
        r += rF(rF, x & ~(1LL), len - 1);
        r += rF(rF, x & ~(2LL), len - 1);
        r += rF(rF, x & ~(4LL), len - 1);
      }
    }
    return r;
  };

  ll N; cin >> N;
  ll S; cin >> S;
  ll x = 7LL;
  string ans;
  REP(i, 0, N) {
    ll a = f(f, x & ~(1LL), N - i - 1);
    DLOGK(i, a, S);
    if (S <= a) {
      ans += 'A';
      x &= ~(1LL);
    }else {
      S -= a;
      ll b = f(f, x & ~(2LL), N - i - 1);
      DLOGK(i, b, S);
      if (S <= b) {
        ans += 'B';
        x &= ~(2LL);
      }else {
        S -= b;
        ll c = f(f, x & ~(4LL), N - i - 1);
        DLOGK(i, c, S);
        if (S <= c) {
          ans += 'C';
          x &= ~(4LL);
        }else {
          cout << -1 << endl;
          return 0;
        }
      }
    }
  }
  cout << ans << endl;

  return 0;
}