#include <bits/stdc++.h>
using namespace std;
const int INF = 1061109567;
const long long LINF = 4557430888798830399ll;
const int MOD = 1000000007;
template <typename T>
void read(T &x) {
  x = 0;
  char c = getchar();
  if (c == EOF) exit(0);
  while (!isdigit(c)) c = getchar();
  while (isdigit(c)) {
    x = x * 10 + (c - '0');
    c = getchar();
  }
  assert(c != EOF);
}
int reads(char *s) {
  int l = 0;
  *s = getchar();
  if (*s == EOF) exit(0);
  while (*s != ' ' && *s != '\t' && *s != '\r' && *s != '\n' && *s != EOF) {
    ++s;
    ++l;
    *s = getchar();
  }
  assert(*s != EOF);
  *s = '\0';
  return l;
}
long long qpow(long long x, long long n) {
  long long res = 1;
  while (n) {
    if (n & 1) res = res * x % MOD;
    x = x * x % MOD;
    n >>= 1;
  }
  return res;
}
char s[305];
int getAnswer(int len) {
  for (int i = 1; i <= len; ++i) putchar(s[i]);
  putchar('\n');
  fflush(stdout);
  int res;
  scanf("%d", &res);
  if (res == 0) exit(0);
  return res;
}
void test_case() {
  int len = 0, res, pres;
  for (int i = 1; i <= 300; ++i) s[i] = 'a';
  res = getAnswer(300);
  len = 300 - res;
  if (len == 0) {
    s[1] = 'b';
    res = getAnswer(1);
    for (int i = 1; i <= res + 1; ++i) s[i] = 'b';
    res = getAnswer(res + 1);
    exit(-1);
  }
  res = getAnswer(len);
  len += res;
  pres = res;
  for (int i = 1; i <= len; ++i) {
    s[i] = 'b';
    res = getAnswer(len);
    if (res >= pres) s[i] = 'a';
    pres = res;
  }
  exit(-1);
}
int main() {
  int t = 1;
  for (int i = 1; i <= t; ++i) {
    test_case();
  }
}
