#include <bits/stdc++.h>
using namespace std;
char s[1000], ans[1000];
namespace judger {
char s[3000], buf[300];
int cnt;
int n;
void init(int _n) {
  n = _n;
  for (int i = 0; i < n; ++i) s[i] = rand() % 2 + 'a';
  printf("spell: %s\n", s);
}
}  // namespace judger
inline void submit(char s[]) {
  printf("%s\n", s);
  fflush(stdout);
}
inline int ask() {
  int x;
  scanf("%d", &x);
  if (x == 0) exit(0);
  return x;
}
int main(int argc, char const *argv[]) {
  memset(s, 'a', 300);
  s[300] = 0;
  submit(s);
  int la = 300 - ask();
  memset(s, 'a', la);
  s[la] = 0;
  if (la == 0) {
    memset(s, 'b', 300);
    submit(s);
    int lb = 300 - ask();
    s[lb] = 0;
    submit(s);
    int x = ask();
    assert(x == 0);
    return 0;
  }
  submit(s);
  int lb = ask(), len = la + lb;
  memset(s, 'a', la + lb);
  s[len] = 0;
  strcpy(ans, s);
  int base = lb;
  for (int i = 0; i < len - 1; ++i) {
    s[i] = 'b';
    submit(s);
    int tans = ask();
    if (tans < base) {
      base = tans;
    } else
      s[i] = 'a';
  }
  if (base > 0) s[len - 1] = 'b';
  printf("%s\n", s);
  return 0;
}
