#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define mod99 998244353
#define mod107 1000000007
#define endl "\n"
#define rep(i,n) for (int i = 0; (i) < (n); ++i)
#define prep(i,a,n) for (int i = (a); i < (n); ++i)
#define rrep(i,n) for (int i = n-1; i >= 0; --i)
#define all(a) a.begin(),a.end()
#define rall(a) a.rbegin(), a.rend()
#define si(x) ((int)(x).size())
//#define YN(bool) if(bool){cout<<"YES"<<endl;}else{cout<<"NO"<<endl;}
#define yn(bool) if(bool){cout<<"Yes"<<endl;}else{cout<<"No"<<endl;}
#define PRE(x) cout << fixed << setprecision(x)
#define YES cout << "Yes\n"
#define NO cout << "No\n"
template <typename T> inline T gcd(T a,T b) {return (b==0)?a:gcd(b,a%b);}
template <typename T> inline T lcm(T a, T b) {return a/gcd(a,b)*b;}
template<class T>bool chmax(T &a, T b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, T b) { if (b<a) { a=b; return 1; } return 0; }
int dx[4]={1,0,-1,0};int dy[4]={0,1,0,-1};using ull = unsigned long long;
string ABC = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
//string abc = "abcdefghijklmnopqrstuvwxyz";
bool issubsquence(string s,string t){
  ll i=0;
  for(char c:t){
    if(i<si(s)&&s[i]==c) i++;
   }
  return i==si(s);
}

int n;
ll s, memo = 0;
string ans = "-1";

void dfs(string S, bool A, bool B, bool C) {
  if(si(S)==n) {
    if(A&&B&&C) {
      memo++;
      if(memo == s) ans = S;
    }
    return;
  }
  if(ans !="-1") return;
  dfs(S+'A',true,B,C);
  dfs(S+'B',A,true,C);
  dfs(S+'C',A,B,true);
}

int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  
  cin >> n >> s;
  dfs("",false,false,false);
  cout << ans << endl;
}