#include <bits/stdc++.h>
using namespace std;
int n, ca = 0, cb = 0;
int main() {
  for (int i = (1), _x = (300); i <= _x; i++) cout << "a";
  cout << endl;
  cin >> ca;
  if (ca == 0) return 0;
  ca = 300 - ca;
  for (int i = (1), _x = (300); i <= _x; i++) cout << "b";
  cout << endl;
  cin >> cb;
  if (cb == 0) return 0;
  cb = 300 - cb;
  n = ca + cb;
  string ans;
  int res;
  for (int i = (1), _x = (n - 1); i <= _x; i++) {
    cout << ans << "a";
    for (int j = (1), _x = (cb); j <= _x; j++) cout << "b";
    cout << endl;
    cin >> res;
    if (res == 0) return 0;
    int bef = n - i - cb;
    if (bef < res)
      ans += 'b', cb--;
    else
      ans += 'a', ca--;
  }
  if (ca > 0)
    ans += 'a';
  else
    ans += 'b';
  cout << ans << endl;
  return 0;
}
