N,M = map(int,input().split())
X = [-float('inf')] + list(map(int,input().split())) + [float('inf')]
A = [0] + list(map(int,input().split())) + [0]
lmin=X[M]-A[M]
rmax=X[M]+A[M]
lindex=M
rindex=M
while lmin<=X[lindex-1] or X[rindex+1]<=rmax:
    if lmin<=X[lindex-1]:
        lindex-=1
        lmin = min(lmin,X[lindex]-A[lindex])
        rmax = max(rmax,X[lindex]+A[lindex])
    if X[rindex+1]<=rmax:
        rindex+=1
        lmin = min(lmin,X[rindex]-A[rindex])
        rmax = max(rmax,X[rindex]+A[rindex])

print(rindex-lindex+1)