#include <bits/stdc++.h>
using namespace std;
int main() {
  ios::sync_with_stdio(false);
  int ans1, ans2, tam;
  cout << 'a' << endl;
  cin >> ans1;
  for (int i = 0; i < ans1; i++) cout << 'b';
  cout << endl;
  cin >> ans2;
  if (ans2 == 0) {
    for (int i = 0; i < ans1; i++) cout << 'b';
    cout << endl;
  } else if (ans1 == ans2 - 1) {
    for (int i = 0; i < ans2; i++) cout << 'a';
    cout << endl;
  } else {
    tam = ans1 + 1;
    char second[501];
    for (int i = 0; i < tam; i++) second[i] = 'b';
    ans1 = ans2;
    for (int j = 0; j < tam; j++) {
      second[j] = 'a';
      for (int i = 0; i < tam; i++) {
        cout << second[i];
      }
      cout << endl;
      cin >> ans2;
      if (ans2 == 0) break;
      if (ans2 >= ans1) second[j] = 'b';
      ans1 = ans2;
    }
  }
}
