package main

import . "fmt"

func main() {
	var x,y string
	Scan(&x,&y)
	if len(x)<len(y) {
		Println("?")
		return
	}
	if len(x)>len(y)+1 {
		Println("?")
		return
	}
	for len(x)>0 {
		Print(x[:1])
		x=x[1:]
		if len(y)>0 {
			Print(y[:1])
			y=y[1:]
		}
	}
	Println()
}