#include <bits/stdc++.h>
using namespace std;
string gen(char c, int n) {
  string ret;
  while (n--) {
    ret.push_back(c);
  }
  return ret;
}
int ask(string s) {
  cout << s << endl;
  int x;
  cin >> x;
  if (x == 0) {
    exit(0);
  }
  return x;
}
int main() {
  int a_cnt = 300 - ask(gen('a', 300));
  int b_cnt = 300 - ask(gen('b', 300));
  string pre = "";
  int n = a_cnt + b_cnt;
  int known = 0;
  while (a_cnt != 0 && b_cnt != 0) {
    int x = ask(pre + "b" + gen('a', n - known - 1));
    if (x == b_cnt - 1) {
      pre += "b";
      --b_cnt;
    } else {
      pre += "a";
      --a_cnt;
    }
    ++known;
  }
  if (a_cnt != 0)
    ask(pre + gen('a', a_cnt));
  else
    ask(pre + gen('b', b_cnt));
  return 0;
}
