bcdef
abbbc
 z
y
 reddit
abcdef
 abc
aaa
 y
z
 cbxz
aaaa

bccdb
 z
 dfdeed
 aab
 y
 abac

#include <bits/stdc++.h>
using namespace std;
template <typename X>
inline bool minimize(X& p, X q) {
  if (p <= q) return 0;
  p = q;
  return 1;
}
template <typename X>
inline bool maximize(X& p, X q) {
  if (p >= q) return 0;
  p = q;
  return 1;
}
const long long inf = 10000000000000;
struct node {
  int x, y;
  bool operator<(const node& oth) const { return x < oth.x; }
};
vector<int> b1, b2;
const int mod = 1000000007;
char s1[100005], s2[100005];
int n, a1[100005], a2[100005];
void doit() {
  scanf("%s%s", s1, s2);
  n = strlen(s1);
  memset(a1, 0, sizeof(a1));
  memset(a2, 0, sizeof(a2));
  for (int i = 0; i <= n - 1; i++) {
    a1[s1[i] - 'a']++;
    a2[s2[i] - 'a']++;
  }
  b1.clear();
  b2.clear();
  for (int i = 0; i <= 25; i++)
    while (a1[i]) {
      b1.push_back(i), a1[i]--;
    }
  for (int i = 25; i >= 0; i--)
    while (a2[i]) {
      b2.push_back(i), a2[i]--;
    }
  int i = 0, j = 0, op = 0, x = 0;
  while (b1[i] < b2[j] && x < n) {
    if (op == 0) {
      printf("%c", b1[i] + 'a');
      i++;
    } else {
      printf("%c", b2[j] + 'a');
      j++;
    }
    op ^= 1;
    x++;
  }
  if (x == n) return;
  if ((n - x) % 2 == 1) op ^= 1;
  while (x < n) {
    if (op == 0) {
      printf("%c", b1[i] + 'a');
      i++;
    } else {
      printf("%c", b2[j] + 'a');
      j++;
    }
    op ^= 1;
    x++;
  }
}
int main() { doit(); }
