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() }