while gets
v=$_.chomp
while 1
(puts"yes";break)if v==""
v=~/^[\(\[\{<]+/
if $&
a,b=$&,$'
a[-1,1]+b[0,1]=~/\(\)|\{\}|\[\]|<>/
if $&
v=a[0..-2]+b[1..-1]
else
v=v.sub!(/^[\(\[\{<]+/,'')==""?"EOL":v
puts"failed at: "+v
break
end
end
end
end