// yukicoder: 871 かえるのうた
// 2019.8.30 bal4u

#include <stdio.h>
#include <string.h>

typedef long long ll;

//// 高速入力
#if 1
#define gc() getchar_unlocked()
#else
#define gc() getchar()
#endif

ll in()   // 整数の入力（負数対応）
{
	ll n = 0; int c = gc();
	if (c == '-') {	c = gc();
		do n = 10*n + (c & 0xf), c = gc(); while (c >= '0');
		return -n;
	}
	do n = 10*n + (c & 0xf), c = gc(); while (c >= '0');
	return n;
}

#define MAX 100005

int q[MAX], top;
ll   X[MAX], A[MAX]; int N;
int  f[MAX];

// 見つからなければ、一つ小さい要素を返す
int bsLE(ll x)
{
	int m, l = 0, r = N;

    while (l < r) {
        m = (l+r) >> 1;
        if (X[m] <= x) l = m + 1; else r = m;
    }
	return l-1;
}

// 見つからなければ、一つ大きい要素を返す
int bsGE(ll x)
{
	int m, l = 0, r = N;

    while (l < r) {
        m = (l+r) >> 1;
        if (X[m] < x) l = m + 1; else r = m;
    }
	return l;
}

int main()
{
	int i, l, r, K, ans; ll w;
	
	N = (int)in(), K = (int)in()-1;
	for (i = 0; i < N; i++) X[i] = in();
	for (i = 0; i < N; i++) A[i] = in();
	
	top = 0, q[top++] = K;
	while (top) {
		i = q[--top], w = X[i] + A[i];
		r = bsLE(X[i] + A[i]);
		if (r >= N) r = N-1;
		l = bsGE(X[i] - A[i]);
		if (l < 0) l = 0;
		for (i = l; i <= r; i++) if (!f[i]) f[i] = 1, q[top++] = i;
	}
	ans = 0; for (i = 0; i < MAX; i++) if (f[i]) ans++;
	printf("%d\n", ans);
	return 0;
}