bcdef
abbbc
 z
y
 reddit
abcdef
 abc
aaa
 y
z
 cbxz
aaaa

bccdb
 z
 dfdeed
 aab
 y
 abac




if __name__ == "__main__" :
	first = list( raw_input() )
	second = list( raw_input() )
	if( len( first ) != len( second ) ) :
		exit( 0 )
	first.sort()
	second.sort()
	second.reverse()
	result = [ '?' for i in first ]
	start = 0
	end = len( result ) - 1
	turn = 0
	while( start <= end ) :
		if( first[ 0 ] > second[ 0 ] ) :
			if turn == 0 :
				result[ end ] = first[ 0 ]
				first.pop( 0 )
			else :
				result[ end ] = second[ 0 ]
				second.pop( 0 )
			end = end - 1
		else :
			if turn == 0 :
				result[ start ] = first[ 0 ]
				first.pop( 0 )
			else :
				result[ start ] = second[ 0 ]
				second.pop( 0 )
			start = start + 1
		turn = ( turn + 1 ) % 2
	print ''.join( result )