#include <bits/stdc++.h>
using namespace std;
void solve() {
  cout << "a"
       << "\n";
  cout.flush();
  long long int i = 0;
  long long int d = 0;
  cin >> d;
  if (d == 0) {
    return;
  }
  long long int n = d + 1;
  long long int arr[n + 1];
  string ret = "";
  string bkup = "";
  for (long long int j = 0; j < n; j++) {
    ret += "a";
  }
  for (long long int j = 0; j < n - 1; j++) {
    bkup += "b";
  }
  if (n != 301) {
    cout << ret << "\n";
    cout.flush();
    cin >> arr[i];
  } else {
    cout << bkup << "\n";
    cout.flush();
    return;
  }
  if (arr[i] == 0) {
    return;
  }
  if (arr[i] == n) {
    cout << bkup << "\n";
    cout.flush();
    return;
  }
  i++;
  for (long long int j = 0; j < n; j++) {
    if (j == n - 1 && ret == bkup + "a") {
      cout << bkup << "\n";
      cout.flush();
      return;
    }
    ret[j] = 'b';
    cout << ret << "\n";
    cout.flush();
    cin >> arr[i];
    if (arr[i] == 0) {
      return;
    } else {
      if (arr[i] >= arr[i - 1]) {
        ret[j] = 'a';
      }
      i++;
    }
  }
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  long long int num = 1;
  for (long long int i = 0; i < num; i++) {
    solve();
  }
}
