#include <bits/stdc++.h>
using namespace std;
int main() {
  string only_a, only_b;
  for (int i = 1; i <= 300; i++) {
    only_a += 'a';
    only_b += 'b';
  }
  cout << only_a << endl;
  int x;
  cin >> x;
  if (x == 0) return 0;
  cout << only_b << endl;
  int y;
  cin >> y;
  if (y == 0) return 0;
  int n = 600 - x - y;
  string sol;
  for (int i = 0; i < n; i++) {
    sol += 'a';
  }
  int cnt_b = x - 300 + n;
  int cnt_a = y - 300 + n;
  if (cnt_a == 0) {
    for (int i = 0; i < n; i++) {
      cout << 'b';
    }
    cout << endl;
    int x;
    cin >> x;
    return 0;
  }
  if (cnt_b == 0) {
    for (int i = 0; i < n; i++) {
      cout << 'a';
    }
    cout << endl;
    int x;
    cin >> x;
    return 0;
  }
  int cur = x - 300 + n;
  for (int i = 0; i < n; i++) {
    sol[i] = 'b';
    int cur2;
    cout << sol << endl;
    cin >> cur2;
    if (cur2 == 0) return 0;
    if (cur < cur2) {
      sol[i] = 'a';
    } else {
      cur = cur2;
    }
  }
  cout << sol << endl;
}
