#include <bits/stdc++.h>
using namespace std;
void out(string s) {
  cout << s << endl;
  cout.flush();
}
int getdist(string i) {
  out(i);
  int res;
  scanf("%d", &res);
  if (res == 0) exit(0);
  return res;
}
string gets(int pos, int length) {
  string s = "";
  for (int i = (0); i < (length); i++) {
    if (i == pos)
      s += "a";
    else
      s += "b";
  }
  return s;
}
int main() {
  int as, bs;
  string s = "";
  for (int i = (0); i < (300); i++) s += "a";
  as = 300 - getdist(s);
  for (int i = (0); i < (300); i++) s[i] = 'b';
  bs = 300 - getdist(s);
  if (as == 0) {
    s = "";
    for (int i = (0); i < (bs); i++) s += "b";
    out(s);
    return 0;
  }
  if (bs == 0) {
    s = "";
    for (int i = (0); i < (as); i++) s += "a";
    out(s);
    return 0;
  }
  int l = as + bs, am = 0;
  string ans = "";
  for (int i = (0); i < (l - 1); i++) {
    if (getdist(gets(i, l)) == (as - 1)) {
      ans += "a";
      am++;
    } else
      ans += "b";
  }
  if (as == am)
    ans += "b";
  else
    ans += "a";
  cout << ans << endl;
}
