@x=[];a=[];@t=[]
n,k = gets.chomp.split(" ").map(&:to_i)
@x+=gets.chomp.split(" ").map(&:to_i)
a+=gets.chomp.split(" ").map(&:to_i)

def max(a,b)
 if a > b
   return a
 elsif b > a
   return b
 else
   return a
 end
end

def min(a,b)
 if a > b
   return b
 elsif b > a
   return a
 else
   return a
 end
end

p=@x[k-1]

l = r = k - 1
ld, rd = @x[k - 1] - a[k - 1], @x[k - 1] + a[k - 1]

updated = true
while(updated)
    updated = false

    while (l - 1 >= 0) and (ld <= @x[l - 1])
        updated = true
        l -= 1
        ld = min(ld, @x[l] - a[l])
        rd = max(rd, @x[l] + a[l])
    end

    while (r + 1 < n) and (rd >= @x[r + 1])
        updated = true
        r += 1
        ld = min(ld, @x[r] - a[r])
        rd = max(rd, @x[r] + a[r])
    end
end

p (r - l + 1)