/* -*- coding: utf-8 -*-
 *
 * 3019.cc:  No.3019 YNeos - yukicoder
 */

#include<cstdio>
#include<cstring>
#include<algorithm>

using namespace std;

/* constant */

const int MAX_N = 100;

/* typedef */

/* global variables */

char x[MAX_N + 4], y[MAX_N + 4];

/* subroutines */

/* main */

int main() {
  scanf("%s%s", x, y);
  int n = strlen(x), m = strlen(y);

  if (m <= n && n <= m + 1) {
    for (int i = 0; i < m; i++) putchar(x[i]), putchar(y[i]);
    if (m < n) putchar(x[n - 1]);
    putchar('\n');
  }
  else
    puts("?");

  return 0;
}