#include <bits/stdc++.h>
using namespace ::std;
const long double PI = acos(-1);
const long long MOD = 1000000000 + 7;
long long gcd(long long a, long long b) { return b == 0 ? a : gcd(b, a % b); }
long long add(long long a, long long b, long long m = MOD) {
  if (a >= m) a %= m;
  if (b >= m) b %= m;
  if (a < 0) a += m;
  if (b < 0) b += m;
  long long res = a + b;
  if (res >= m or res <= -m) res %= m;
  if (res < 0) res += m;
  return res;
}
long long mul(long long a, long long b, long long m = MOD) {
  if (a >= m) a %= m;
  if (b >= m) b %= m;
  if (a < 0) a += m;
  if (b < 0) b += m;
  long long res = a * b;
  if (res >= m or res <= -m) res %= m;
  if (res < 0) res += m;
  return res;
}
long long pow_mod(long long a, long long b, long long m = MOD) {
  long long res = 1LL;
  a = a % m;
  while (b) {
    if (b & 1) res = mul(res, a, m);
    b >>= 1;
    a = mul(a, a, m);
  }
  return res;
}
long long fastexp(long long a, long long b) {
  long long res = 1LL;
  while (b) {
    if (b & 1) res = res * a;
    b >>= 1;
    a *= a;
  }
  return res;
}
int gcdExtendido(int a, int b, int *x, int *y) {
  if (a == 0) {
    *x = 0;
    *y = 1;
    return b;
  }
  int x1, y1;
  int gcd = gcdExtendido(b % a, a, &x1, &y1);
  *x = y1 - (b / a) * x1;
  *y = x1;
  return gcd;
}
int modInverso(int a, int m) {
  int x, y;
  int g = gcdExtendido(a, m, &x, &y);
  if (g != 1)
    return -1;
  else
    return (x % m + m) % m;
}
int n;
int interact(string &s) {
  printf("%s\n", s.c_str());
  fflush(stdout);
  int ans;
  cin >> ans;
  return ans;
}
int main() {
  string act = "a";
  for (int i = 1; i < 300; i++) act.push_back('a');
  int l1 = interact(act);
  if (l1 == 0) return 0;
  act = "b";
  for (int i = 1; i < 300; i++) act.push_back('b');
  int l2 = interact(act);
  if (l2 == 0) return 0;
  n = 600 - l1 - l2;
  string ans = "";
  for (int i = 0; i < n; i++) ans.push_back('a');
  if (l2 == 300) {
    interact(ans);
    return 0;
  }
  l2 = 300 - l2;
  for (int i = 0; i < n; i++) {
    ans[i] = 'b';
    int len = interact(ans);
    if (len == 0) return 0;
    if (len >= l2) {
      ans[i] = 'a';
    } else {
      l2 -= 1;
    }
  }
  return 0;
}
