#include<stdio.h>
int main()
{
	char x[102], y[102];
	scanf("%s%s", x, y);
	int i;
	int n, m;
	for (n = 0; x[n] != '\0'; n++);
	for (m = 0; y[m] != '\0'; m++);
	if (n == m)
	{
		for (i = 0; i < n; i++)
			printf("%c%c", x[i], y[i]);
		printf("\n");
	}
	else if (n == m + 1)
	{
		for (i = 0; i < m; i++)
			printf("%c%c", x[i], y[i]);
		printf("%c\n", x[i]);
	}
	else
		printf("?\n");
	return 0;
}