from bisect import bisect_left, bisect, insort_left, insort
def solve():
    n, k = map(int, input().split())
    k -= 1
    X = list(map(int, input().split()))
    A = list(map(int, input().split()))
    L = [X[i] - A[i] for i in range(n)]
    R = [X[i] + A[i] for i in range(n)]
    l = r = k
    flg = True
    min_x, max_x = L[k], R[k]
    while flg:
        flg = False
        lt = bisect_left(X, min_x)
        rt = bisect(X, max_x) - 1
        min_x = min(min_x, min(L[lt:l + 1]), min(L[r :rt + 1]))
        max_x = max(max_x, max(R[lt:l + 1]), max(R[r :rt + 1]))
        if l != lt or r != rt:
            l, r, flg = lt, rt, True
    print(r - l + 1)
solve()