#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
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; }
#define vi vector<int>
#define vl vector<ll>
#define vii vector<pair<int,int>>
#define vll vector<pair<ll,ll>>
#define vvi vector<vector<int>>
#define vvl vector<vector<ll>>
#define vvii vector<vector<pair<int,int>>>
#define vvll vector<vector<pair<ll,ll>>>
#define vst vector<string>
#define pii pair<int,int>
#define pll pair<ll,ll>
#define pb push_back
#define all(x) (x).begin(),(x).end()
#define mkunique(x) sort(all(x));(x).erase(unique(all(x)),(x).end())
#define fi first
#define se second
#define mp make_pair
#define si(x) int(x.size())
const int mod=998244353,MAX=300005,INF=15<<26;

string S;
int CN[3];
int N;
vst X;

void DFS(){
    if(si(S)==N){
        if(CN[0]&&CN[1]&&CN[2]){
            X.pb(S);
        }
        return;
    }
    for(char c='A';c<='C';c++){
        CN[c-'A']++;
        S+=c;
        DFS();
        S.pop_back();
        CN[c-'A']--;
    }
}

int main(){
    
    std::ifstream in("text.txt");
    std::cin.rdbuf(in.rdbuf());
    cin.tie(0);
    ios::sync_with_stdio(false);
    
    cin>>N;
    int XX;cin>>XX;
    DFS();
    if(si(X)>=XX) cout<<X[XX-1]<<endl;
    else cout<<-1<<endl;
    
}