#include <bits/stdc++.h>
using namespace std;
#include <atcoder/all>
using namespace atcoder;
using ll=long long;
using Graph=vector<vector<int>>;
#define INF 1000000000
#define MOD 998244353
#define MAX 1000000

int main(){
  int N,K;
  cin>>N>>K;
  vector<pair<int,int>> diff(N);
  for(int i=0;i<N;i++){
    int A,B;
    cin>>A>>B;
    diff[i].first=B-A;
    diff[i].second=i;
  }
  sort(diff.begin(),diff.end());

  vector<char> ans(N,'B');
  for(int i=0;i<K;i++){
    ans[diff[i].second]='A';
  }
  for(int i=0;i<N;i++){
    cout<<ans[i];
  }
  cout<<'\n';

}