#include <bits/stdc++.h>
using namespace std;
int ask(string s) {
  cout << s << '\n';
  cout.flush();
  int res;
  cin >> res;
  if (res == 0) exit(0);
  return res;
}
int main() {
  int n = ask("b") + 1;
  string s;
  for (int i = 0; i < n - 1; ++i) s += 'a';
  int cntB = ask(s);
  s += "a";
  int cntA = 0;
  string ans = s;
  for (int i = 0; i < n - 1; ++i) {
    s[i] = 'b';
    if (ask(s) < cntB)
      ans[i] = 'b';
    else
      ++cntA;
    s[i] = 'a';
  }
  if (cntA == n - cntB) ans[n - 1] = 'b';
  ask(ans);
}
