X=input()
Y=input()


if len(X)==len(Y):
  ans=[]
  for i in range(len(X)):
    ans.append(X[i])
    ans.append(Y[i])
  print(''.join(ans))
elif len(X)==len(Y)+1:
  ans=[]
  for i in range(len(Y)):
    ans.append(X[i])
    ans.append(Y[i])
  ans.append(X[-1])
  print(''.join(ans))
else:
  print('?')