n,m=gets.split.map &:to_i
x={}
y={}
m.times{
  b=gets.split.map(&:to_i)
  c=b[0]
  x[c]=[] unless x[c]
  x[c]<<b[1]
  c=b[1]
  y[c]=[] unless y[c]
  y[c]<<b[0]
}
r=0
x.keys.sort{|a,b|b<=>a}.each{|v|
  if x[v].size>0
    r|=2**v
    y[v].each{|i|
      x[i].delete v
    } if y[v]
  end
}
puts r.to_s(2)