#include <bits/stdc++.h>
using namespace std;
using namespace chrono;
#if __has_include(<atcoder/all>)
#include <atcoder/all>
using namespace atcoder;
#endif

int main()
{
    int64_t n, s;
    cin >> n >> s;
    s--;

    vector<string> ss;

    auto powi = [](int64_t a, int64_t n) -> int64_t
    {
        int64_t ret = 1;
        for (; n; n >>= 1)
        {
            if (n & 1)
            {
                ret *= a;
            }
            a *= a;
        }
        return ret;
    };

    for (int64_t S = 0; S < powi(3, n); S++)
    {
        string t;
        bool a = false, b = false, c = false;
        for (int64_t i = 0, T = S; i < n; i++)
        {
            t += "ABC"[T % 3];
            a |= T % 3 == 0;
            b |= T % 3 == 1;
            c |= T % 3 == 2;
            T /= 3;
        }

        if (a && b && c)
        {
            ss.push_back(t);
        }
    }

    ranges::sort(ss);

    if (s < ss.size())
    {
        cout << ss[s] << endl;
    }
    else
    {
        cout << -1 << endl;
    }

    return 0;
}