题目传送门

#include<iostream>
#include<string>
using namespace std;
string s="AB";
int n,q;
int l,r;
char c;
int main(){
  cin>>n>>q;
  cout<<"? A B"<<endl;
  cin>>c;
  if(c=='>')
    s="BA";
  for(int i=3;i<=n;++i){
    l=0,r=s.size();
    while(r-l>1){
      int mid=(l+r)/2;
      cout<<"? "<<char('A'+i-1)<<' '<<s[mid]<<endl;
      cin>>c;
      if(c=='>')
        l=mid;
      else
        r=mid;
    }
    string ss;
    ss+='A'+i-1;
    s.insert(l,ss);
  }
  cout<<"! "<<s<<endl;
}