#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, a, b, dist1, dist2, i, blank;
  string s, t;
  for (i = 0; i < 300; i++) cout << "a";
  cout << endl;
  cin >> dist1;
  if (dist1 == 0) return 0;
  for (i = 0; i < 300; i++) cout << "b";
  cout << endl;
  cin >> dist2;
  if (dist2 == 0) return 0;
  blank = dist1 + dist2 - 300;
  dist1 -= blank;
  dist2 -= blank;
  n = dist1 + dist2;
  s = "";
  for (i = 0; i < n; i++) s += "a";
  if (dist2 == n) {
    cout << s << endl;
    cin >> dist2;
    return 0;
  }
  for (i = 0; i < n - 1; i++) {
    t = s;
    t[i] = 'b';
    cout << t << endl;
    cin >> dist2;
    if (dist2 == 0) return 0;
    if (dist2 < dist1) s[i] = 'b';
    dist1 = min(dist2, dist1);
  }
  s[n - 1] = 'b';
  cout << s << endl;
  cin >> dist2;
  return 0;
}
