#include <bits/stdc++.h>
using namespace std;
int Ask(string s) {
  cout << s << '\n';
  cout.flush();
  int diff;
  cin >> diff;
  if (diff == 0) exit(0);
  return diff;
}
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  if (fopen("input.txt", "r")) {
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
  }
  int n = Ask("b") + 1;
  if (n > 300) {
    string s = "";
    for (int i = 1; i < (int)n; ++i) s += 'a';
    Ask(s);
  }
  string s = "";
  for (int i = 1; i <= (int)n; ++i) s += 'b';
  int cur = Ask(s);
  if (cur == n) {
    s = "";
    for (int i = 1; i < (int)n; ++i) s += 'a';
    int ok = Ask(s);
    assert(ok == 0);
    return 0;
  }
  string ans = s;
  for (int pos = 0; pos < (int)n; ++pos) {
    s = ans;
    s[pos] = 'a';
    int tmp = Ask(s);
    if (tmp < cur) ans[pos] = 'a', cur = tmp;
  }
  return 0;
}
