#include <bits/stdc++.h>
using namespace std;
int main() {
  cout << "a" << endl;
  long long length, i, j;
  cin >> length;
  if (length == 0) return 0;
  length++;
  if (length > 300) {
    for (i = 0; i < 300; i++) {
      cout << "b";
    }
    cout << endl;
    long long p;
    cin >> p;
    return 0;
  }
  for (i = 0; i < length; i++) cout << "a";
  cout << endl;
  long long ret;
  cin >> ret;
  if (ret == 0)
    return 0;
  else if (ret == length) {
    for (i = 0; i < ret - 1; i++) cout << "b";
    cout << endl;
    long long take;
    cin >> take;
    return 0;
  } else {
    vector<char> c;
    for (i = 0; i < length; i++) {
      c.push_back('a');
    }
    for (i = 0; i < length; i++) {
      c[i] = 'b';
      for (j = 0; j < length; j++) cout << c[j];
      cout << endl;
      long long take;
      cin >> take;
      if (take >= ret)
        c[i] = 'a';
      else
        ret = take;
      if (ret == 0) return 0;
    }
  }
  return 0;
}
