#include <bits/stdc++.h>
using namespace std;
const long long mod = 1000000007;
const long long inf = 1ll << 50;
const long long maxn = 100005;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout << "a" << endl;
  long long x;
  cin >> x;
  if (x == 300) {
    cout << string(300, 'b') << endl;
    return 0;
  }
  cout << string(x + 1, 'a') << endl;
  long long cur;
  cin >> cur;
  if (cur > x) {
    cout << string(x, 'b') << endl;
    return 0;
  }
  if (cur == 0) {
    cout << string(x + 1, 'a') << endl;
    return 0;
  } else {
    string res = string(x + 1, 'a');
    int len = x + 1;
    long long tmp;
    for (int i = len - 1; i >= 0; i--) {
      res[i] = 'b';
      cout << res << endl;
      cin >> tmp;
      if (tmp == 0) {
        return 0;
      }
      if (tmp > cur) {
        res[i] = 'a';
      } else {
        cur = tmp;
      }
    }
  }
  return 0;
}
