#include <bits/stdc++.h>
using namespace std;
void solve() {
  auto q = [](string s) {
    cout << s << endl;
    int x;
    cin >> x;
    if (x == 0) exit(0);
    return x;
  };
  int a = 300 - q(string(300, 'a'));
  int b = 300 - q(string(300, 'b'));
  string s;
  int d;
  if (a > b) {
    s = string(a + b, 'a');
    d = b;
  } else {
    s = string(a + b, 'b');
    d = a;
  }
  if (d == 0) {
    cout << s;
    exit(0);
  }
  int n = a + b;
  auto flip = [](char& x) { x = (x == 'a' ? 'b' : 'a'); };
  for (int i = 0; i < n - 1; i++) {
    flip(s[i]);
    int x = q(s);
    if (x > d)
      flip(s[i]);
    else
      d = x;
  }
  if (d > 0) flip(s[n - 1]);
  cout << s;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  solve();
  cout << endl;
}
