#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
#define rep(i,n) for(int i = 0; i <n; i++)
#define all(a) a.begin(),a.end()
#define SORT(a) sort(all(a));
#define MIN(a) *min_element(all(a))
#define MAX(a) *max_element(all(a))
#define SUM(a) accumulate(all(a),0LL)
using ll=long long;
using ld=long double;
using ull=unsigned long;
ll MOD=998244353;
const int dx[]={0,1,0,-1,1,-1,1,-1};const int dy[]={1,0,-1,0,1,1,-1,-1};
const string ALPHA="ABCDEFGHIJKLMNOPQRSTUVWXYZ";const string alpha="abcdefghijklmnopqrstuvwxyz";
using Graph = vector<vector<int>>;
int main(){
  cin.tie(nullptr);
  cout.tie(nullptr);
  ios::sync_with_stdio(false);
  ll N;cin>>N;
  ll cnt=0;
  string ans="";
  rep(i,N){ans+='a';}
  while(cnt!=N){
  	ll now=0;
  	ll f;
  	while(true){
  		ans[cnt]=alpha[now];
  		cout<<'?'<<" "<<ans;
  		ll res;cin>>res;
  		if(now==0){f=res;continue;}
  		else if(now==25){break;}
  		else{
  			if(res==f+1){
  				break;
  			}
  			else if(res=f-1){
  				ans[cnt]='a';
  				break;
  			}
  		}
  		cnt++;
  	}
  }
  cout<<ans<<endl;
}