#include <bits/stdc++.h>
using namespace std;
signed main() {
  string s = "";
  cout << "a" << endl;
  cout.flush();
  long long a1;
  cin >> a1;
  cout.flush();
  if (a1 == 0) {
    return 0;
  }
  for (long long i = 0; i < a1; i++) {
    s.push_back('b');
  }
  cout << s << endl;
  cout.flush();
  long long a2;
  cin >> a2;
  cout.flush();
  if (a2 != 0) {
    s.push_back('b');
    for (long long i = 0; i <= a1; i++) {
      s[i] = 'a';
      cout << s << endl;
      cout.flush();
      long long an;
      cin >> an;
      cout.flush();
      if (an == 0) {
        return 0;
      }
      if (an < a2) {
        a2 = an;
        s[i] = 'a';
      } else {
        s[i] = 'b';
      }
    }
    cout << s;
    cout.flush();
  }
}
