import sys
import pypyjit
import itertools
import heapq
import math
from collections import deque, defaultdict
import bisect

input = sys.stdin.readline
sys.setrecursionlimit(10 ** 6)
pypyjit.set_param('max_unroll_recursion=-1')


def index_lt(a, x):
    'return largest index s.t. A[i] < x or -1 if it does not exist'
    return bisect.bisect_left(a, x) - 1


def index_le(a, x):
    'return largest index s.t. A[i] <= x or -1 if it does not exist'
    return bisect.bisect_right(a, x) - 1


def index_gt(a, x):
    'return smallest index s.t. A[i] > x or len(a) if it does not exist'
    return bisect.bisect_right(a, x)


def index_ge(a, x):
    'return smallest index s.t. A[i] >= x or len(a) if it does not exist'
    return bisect.bisect_left(a, x)


N, K = map(int, input().split())
X = list(map(int, input().split()))
A = list(map(int, input().split()))
K -= 1

l = X[K]
r = X[K]
li = K
ri = K
for i in range(K, -1, -1):
    if X[i] < l:
        break
    l = min(l, X[i] - A[i])
    li -= 1
for i in range(K, N):
    if r < X[i]:
        break
    r = max(r, X[i] + A[i])
    ri += 1
# li < x < ri
print(ri - li - 1)