#include <bits/stdc++.h>
using namespace std;
void print(char a[], int n) {
  for (int i = 0; i < n; i++) cout << a[i];
  cout << "\n";
  cout.flush();
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  char temp[305];
  int r[305];
  int turns = 0;
  for (int i = 0; i < 300; i++) temp[i] = 'a';
  print(temp, 300);
  cin >> r[turns];
  if (r[turns] == 0) {
    exit(0);
  }
  turns++;
  for (int i = 0; i < 300; i++) temp[i] = 'b';
  print(temp, 300);
  cin >> r[turns];
  if (r[turns] == 0) {
    exit(0);
  }
  turns++;
  int n = 600 - r[0] - r[1];
  int cnta = r[1] - 300 + n;
  int cntb = r[0] - 300 + n;
  if (cnta == 0) {
    for (int i = 0; i < n; i++) temp[i] = 'b';
    print(temp, n);
    cin >> r[turns];
    exit(0);
  } else if (cntb == 0) {
    for (int i = 0; i < n; i++) temp[i] = 'a';
    print(temp, n);
    cin >> r[turns];
    exit(0);
  }
  for (int i = 0; i < n; i++) temp[i] = 'a';
  temp[0] = 'b';
  int last = 0, cur = 1, i = 0;
  while (turns < n + 3) {
    temp[i] = 'b';
    print(temp, n);
    cin >> r[turns];
    if (!r[turns]) {
      exit(0);
    }
    if (r[turns] == cntb - cur)
      cur++;
    else
      temp[i] = 'a';
    i++;
    turns++;
  }
  return 0;
}
