import bisect

n, k = map(int,input().split())
X = list(map(int,input().split()))
A = list(map(int,input().split()))

r = [0]*n    
r[k-1] = 1

L = [X[k-1]-A[k-1]]
R = [X[k-1]+A[k-1]]
lprev, rprev = n-1, 0
left, right = 0, n-1

while True:
    left = bisect.bisect_left(X,min(L))
    right = min(n-1,bisect.bisect_left(X,max(R)))

    if X[right] != max(R):
        right -= 1
    L = []
    R = []
    for i in range(left,right+1):
        r[i] = 1
        L.append(X[i]-A[i])
        R.append(X[i]+A[i])
    
    tmpl,lprev = lprev, min(left,lprev)
    tmpr,rprev = rprev, min(right,rprev)
    if tmpl == lprev and tmpr == rprev:
        break

print(sum(r))