// #define _GLIBCXX_DEBUG
#include <bits/stdc++.h>
using namespace std;
#define rep(i, a, b) for(long long i = (a); i < (b); i++) // [a, b)を昇順に
#define drep(i, a, b) for(long long i = (b) - 1; i >= a; i--) // [a, b)を降順に
#define all(v) v.begin(), v.end() // 昇順sortに
#define rall(v) v.rbegin(), v.rend() // 降順sortに
#define sz(x) (int)(x).size()
#define decimal(n) cout << fixed << setprecision(n);
#define debug(x) cerr << #x << " = " << x << endl;
#define Yes cout << "Yes" << endl
#define No cout << "No" << endl
#define yesno(condition) { if (condition) cout << "Yes" << endl; else cout << "No" << endl; }
using vi = vector<int>; using vvi = vector<vi>; using vs = vector<string>;
using ll = long long; using vl = vector<ll>; using vvl = vector<vl>; using vvvl = vector<vvl>;
// #include <atcoder/all>
// using namespace atcoder;
// using mint = modint998244353;
// using vm = vector<mint>; using vvm = vector<vm>; using vvvm = vector<vvm>;
const ll MOD = 998244353;
// using mint = modint;
// const ll MOD = 998244353;
// using mint = modint1000000007;
// const ll MOD = 1000000007;
using P = pair<ll, ll>; using T = tuple<ll, ll, ll>;
const ll MAX = 2000100; const ll llINF = 2e18;
const int intINF = 2e9; const long double pi = acos(-1);
ll di[] = {0, -1, 0, 1, -1, -1, 1, 1};
ll dj[] = {1, 0, -1, 0, 1, -1, -1, 1};
template<class T>bool chmax(T& a, const T& b) { if (a < b) { a = b; return 1; } return 0; }
template<class T>bool chmin(T& a, const T& b) { if (b < a) { a = b; return 1; } return 0; }
template<class T> using pq = priority_queue<T, vector<T>>; //大きい順
template<class T> using pq_g = priority_queue<T, vector<T>, greater<T>>; //小さい順

bool isin(ll i, ll j, ll n, ll m) { return (0 <= i && i < n && 0 <= j && j < m); }

/**
 * Read a vector from input. Set start to 1 if you want it to be 1-indexed.
 */
template<typename T>
vector<T> read_vector(int N, int start = 0) {
    vector<T> v(start + N);
    for (int i = start; i < (int)v.size(); i++) {
        std::cin >> v[i];
    }
    return v;
}
/**
 * Read a matrix from input. Set start_l to make lines 1-indexed. Same thing for start_c.
 */
template<typename T>
vector<vector<T>> read_matrix(int N, int M, int start_l = 0, int start_c = 0) {
    vector<vector<T>> matr = create_matrix<T>(N + start_l, M + start_c);

    for (int l = start_l; l < N + start_l; l++)
        for (int c = start_c; c < M + start_c; c++)
            std::cin >> matr[l][c];

    return matr;
}
template<class T, size_t n, size_t idx = 0>
auto make_vec(const size_t (&d)[n], const T& init) noexcept {
    if constexpr (idx < n) return std::vector(d[idx], make_vec<T, n, idx + 1>(d, init));
    else return init;
}
template<class T, size_t n>
auto make_vec(const size_t (&d)[n]) noexcept {
    return make_vec(d, T{});
}
// 配列の要素を空白区切りで出力 第二引数をtrueにすると改行区切り
template<typename T> inline void print_vec(const vector<T> &v, bool split_line=false) {
    constexpr bool isValue = is_integral<T>::value;
    for (int i = 0; i < (int)v.size(); i++) {
        if constexpr(isValue){
            if((v[i]==intINF) || (v[i]==llINF)) cout << 'x' << " \n"[split_line || i+1==(int)v.size()];
            else cout << v[i] << " \n"[split_line || i+1==(int)v.size()];
        }else cout << v[i] << " \n"[split_line || i+1==(int)v.size()];
    }
}

// DFSで長さnの0,1,2列を全て生成するコード
// 3^n 通りの全探索ができる
 

ll n;
ll num[12];
vector<string> arr;

void dfs(ll depth) {
    if(depth == n) {
        ll bit = 0;
        string s = "";
        rep(i, 0, n) {
            s += ('A' + num[i]);
            bit |= (1 << num[i]);
        }

        if(bit != (1 << 3) - 1) return ;

        arr.push_back(s);
        return;
    }

    rep(i, 0, 3) {
        num[depth] = i;
        dfs(depth + 1);
    }
}


int main() {
    ll x;
    cin >> n >> x;
    x--;

    dfs(0);
    sort(all(arr));

    if(sz(arr) < x + 1) {
        cout << -1 << endl;
        return 0;
    }
    cout << arr[x] << endl;
}