#include <bits/stdc++.h>
#pragma GCC optimize("O3")
#pragma GCC target(sse, sse2, sse3, popcnt, tune = native)
using namespace std;
const long long MAXN = 4e5 + 47, inf = 1e9 + 47;
void read() {
  cout << "a" << endl;
  long long cnt1 = 0;
  cin >> cnt1;
  if (cnt1 == 0) return;
  string ans = "";
  for (long long i = 0; i < cnt1 + 1; ++i) ans += 'a';
  if ((long long)ans.size() > 300) {
    ans = "";
    for (long long i = 0; i < 300; ++i) ans += 'b';
    cout << ans << endl;
    return;
  }
  cout << ans << endl;
  long long cnt2 = 0;
  cin >> cnt2;
  if (cnt2 > cnt1) {
    ans = "";
    for (long long i = 0; i < cnt2 - 1; ++i) ans += 'b';
    cout << ans << endl;
    cin >> cnt2;
    return;
  }
  if (cnt2 == 0) return;
  vector<long long> k;
  for (long long i = 0; i < cnt1; ++i) {
    ans[i] = 'b';
    cout << ans << endl;
    long long cnt3 = 0;
    cin >> cnt3;
    if (cnt3 + 1 == cnt2) k.push_back(i);
    ans[i] = 'a';
  }
  for (long long c : k) ans[c] = 'b';
  if ((long long)k.size() != cnt2) ans.back() = 'b';
  cout << ans << endl;
  cin >> cnt2;
}
void solve() {}
signed main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  long long t = 1;
  while (t--) {
    read();
    solve();
  }
}
