#include <bits/stdc++.h>
using namespace std;
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  cout << "a" << endl;
  int n;
  cin >> n;
  if (n == 0) return 0;
  if (n == 300) {
    for (int i = 1; i <= 100; i++) {
      cout << "bbb";
    }
    cout << endl;
    cin >> n;
    return 0;
  }
  for (int i = 1; i <= n + 1; i++) {
    cout << 'a';
  }
  cout << endl;
  int u;
  cin >> u;
  if (u == 0) return 0;
  if (u == n + 1) {
    for (int i = 1; i <= n; i++) {
      cout << "b";
    }
    cout << endl;
    cin >> u;
    return 0;
  }
  string s;
  for (int i = 1; i <= n + 1; i++) {
    s += "a";
  }
  for (int i = 0; i <= n; i++) {
    s[i] = 'b';
    cout << s << endl;
    int foo;
    cin >> foo;
    if (foo > u)
      s[i] = 'a';
    else
      u = foo;
    if (foo == 0) return 0;
  }
  return 0;
}
