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

#define all(v) v.begin(),v.end()
using ll = long long;
using ull = unsigned long long;
using lll = __int128;
using vll=vector<ll>;
using vvll = vector<vector<ll>>;
using P = pair<ll,ll>;
using vp=vector<pair<ll, ll>>;
//using mint=modint1000000007;
//using mint=modint998244353;

const ll INF=1ll<<60;
ll mod10=1e9+7;
ll mod99=998244353;
const double PI = acos(-1);

#define rep(i,n) for (ll i=0;i<n;++i)
#define per(i,n) for(ll i=n-1;i>=0;--i)
#define rep2(i,a,n) for (ll i=a;i<n;++i)
#define per2(i,a,n) for (ll i=a;i>=n;--i)

template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return true; } return false; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return true; } return false; }

bool solve(){
    ll N;cin>>N;
    ll M;cin>>M;
    ll cnt=0;
    auto dfs = [&](auto&& dfs,ll now,string S) -> void {
        if(now==N){
            string s=S;
            sort(all(S));
            S.erase(unique(all(S)),S.end());
            if(S.size()<3) return;
            cnt++;
            if(cnt==M){
                cout<<s<<endl;
                exit(0);
            }
            return;
        }
        S+='A';
        dfs(dfs,now+1,S);
        S.back()='B';
        dfs(dfs,now+1,S);
        S.back()='C';
        dfs(dfs,now+1,S);
    };
    dfs(dfs,0,"");
    cout << -1 << endl;
    return 0;

}




int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    ll T=1;//cin>>T;
    rep(i,T) solve();
}