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

#define For(i, a, b) for(int i = (a); i < (b); i++)
#define rep(i, n) For(i, 0, n)
#define rFor(i, a, b) for(int i = (a); i >= (b); i--)
#define ALL(v) (v).begin(), (v).end()
#define rALL(v) (v).rbegin(), (v).rend()
#define SZ(v) ((int)(v).size())

using lint = long long;
using ld = long double;

int INF = 2000000000;
lint LINF = 1000000000000000000;

struct SetupIo {
    SetupIo() {
        ios::sync_with_stdio(false);
        cin.tie(nullptr);
        cout << fixed << setprecision(15);
        cerr << fixed << setprecision(15);
    }
} setupio;

int main() {
    int n, s;
    cin >> n >> s;
    vector<string> vec;

    auto kind = [](string s) -> int {
        int res = 0;
        if (count(ALL(s), 'A')) { res++; }
        if (count(ALL(s), 'B')) { res++; }
        if (count(ALL(s), 'C')) { res++; }
        return res;
    };

    auto f = [&](auto f, const string s) -> void {
        if (SZ(s) == n - 1 && kind(s) == 1) {
            return;
        }
        if (SZ(s) == n) {
            if (kind(s) == 3) {
                vec.emplace_back(s);
            }
            return;
        }
        f(f, s + 'A');
        f(f, s + 'B');
        f(f, s + 'C');
    };

    f(f, "");

    sort(ALL(vec));
    vec.erase(unique(ALL(vec)), vec.end());

    cout << (s <= SZ(vec) ? vec[s - 1] : "-1") << "\n";
}