#include <bits/stdc++.h>
using namespace std;
const int N = 2e5 + 10;
const long long inf = 2e16;
int arr[310];
int main() {
  string ans = "";
  printf("a\n");
  fflush(stdout);
  int num;
  scanf("%d", &num);
  if (num == 300) {
    for (int i = 1; i <= 300; i++) printf("b");
    printf("\n");
    fflush(stdout);
    scanf("%d", &num);
    exit(0);
  }
  if (num == 0) exit(0);
  for (int i = 0; i <= num; i++) printf("a");
  printf("\n");
  fflush(stdout);
  int pre;
  scanf("%d", &pre);
  if (pre >= num + 1) {
    for (int i = 1; i <= num; i++) printf("b");
    printf("\n");
    fflush(stdout);
    scanf("%d", &num);
    exit(0);
  } else {
    for (int i = 1; i <= num + 1; i++) {
      cout << ans;
      printf("b");
      for (int j = i + 1; j <= num + 1; j++) printf("a");
      cout << endl;
      fflush(stdout);
      int now;
      scanf("%d", &now);
      if (now == 0) exit(0);
      if (now > pre)
        ans += "a";
      else
        ans += "b", pre = now;
    }
  }
  return 0;
}
