#input of int(split by space)
def get_i()
  return gets.chomp.split(" ").map(&:to_i)
end
#input of float(split by space)
def get_f()
  return gets.chomp.split(" ").map(&:to_f)
end
#input of string(split by space)
def get()
  return gets.chomp.split(" ")
end
#input of string(split per one character)
def get_nsp()
  return gets.chomp.split("")
end
#yes or no decision
def yn_judge(bool,y="Yes",n="No")
  return bool ? y : n 
end
#create of array
def array(size1,init=nil,size2=-1)
  if size2==-1
    return Array.new(size1){init}
  else
    return Array.new(size2){Array.new(size1){init}}
  end
end

def max(a,b)
    return a>b ? a : b
end

def min(a,b)
    return a>b ? b : a
end

INF=Float::INFINITY

N=gets.to_i
a=get_i
b=get_i
r=0
if a.inject(:+)<b.inject(:+)
    puts -1
    exit
end
dif=array(N)
N.times do|i|
    dif[i]=a[i]-b[i]
end
ans=0
neg=dif.select{|x| x<0}
ans+=neg.size
sum=neg.inject(0){|res,x| res-=x}
dif.sort{|x,y| y<=>x}.each do|d|
    if sum<=0
        break
    end
    sum-=d
    ans+=1
end
puts ans