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)


class SegTree:
    def __init__(self, N, func, e):
        self.N = N
        self.func = func
        self.X = [e] * (N << 1)
        self.e = e

    def build(self, seq):
        for i in range(self.N):
            self.X[self.N + i] = seq[i]
        for i in range(self.N)[::-1]:
            self.X[i] = self.func(self.X[i << 1], self.X[i << 1 | 1])

    def add(self, i, x):
        i += self.N
        self.X[i] += x
        while i > 1:
            i >>= 1
            self.X[i] = self.func(self.X[i << 1], self.X[i << 1 | 1])

    def update(self, i, x):
        i += self.N
        self.X[i] = x
        while i > 1:
            i >>= 1
            self.X[i] = self.func(self.X[i << 1], self.X[i << 1 | 1])

    def query(self, L, R):
        L += self.N
        R += self.N
        vL = self.e
        vR = self.e
        while L < R:
            if L & 1:
                vL = self.func(vL, self.X[L])
                L += 1
            if R & 1:
                R -= 1
                vR = self.func(self.X[R], vR)
            L >>= 1
            R >>= 1
        return self.func(vL, vR)


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

left = []
right = []
for i in range(N):
    l = index_ge(X, X[i] - A[i])
    r = index_le(X, X[i] + A[i])
    left.append(l)
    right.append(r)

INF = 1 << 60
lst = SegTree(N, min, INF)
rst = SegTree(N, max, -INF)
lst.build(left)
rst.build(right)

E = [None] * N
for i in range(N):
    l = lst.query(left[i], right[i] + 1)
    r = rst.query(left[i], right[i] + 1)
    E[i] = (max(l, 0), min(r, N - 1))

dq = deque([K])
visited = [False] * N
l = INF
r = -INF
while len(dq) > 0:
    v = dq.popleft()
    if visited[v] is True:
        continue
    visited[v] = True
    l = min(l, v)
    r = max(r, v)

    for d in E[v]:
        if visited[d] is False:
            dq.append(d)
print(r - l + 1)