#include <bits/stdc++.h>

using namespace std;
using ll = long long;
using ull = unsigned long long;

#ifndef __MACRO_H__
#define __MACRO_H__

#define all(collection)  (collection).begin(), (collection).end()		// begin to end
#define rep(i, begin, end) for (ll i = begin; i < end; i++)				// repeat
#define repr(i, begin, end) for (ll i = begin; end < i; i--)			// repeat reverse
#define size(collection) ((ll) (collection).size())						// collection size

#endif

int main(void)
{
	ll n, k; cin >> n >> k; k--;
	vector<ll> x(n), a(n);
	rep(i, 0, n)
		cin >> x[i];
	rep(i, 0, n)
		cin >> a[i];

	ll minx = x[k] - a[k];
	ll maxx = x[k] + a[k];
	ll li = k;
	ll ri = k;
	while(1)
	{
		if ((li == 0 || x[li - 1] < minx) && (ri == n - 1 || maxx < x[ri + 1]))
			break;

		if (0 <= li - 1 && minx <= x[li - 1])
			li--;
		if (ri + 1 <= n - 1 && x[ri + 1] <= maxx)
			ri++;

		minx = min({ minx, x[li] - a[li], x[ri] - a[ri] });
		maxx = max({ maxx, x[li] + a[li], x[ri] + a[ri] });
	}

	ll ans = 0;
	rep(i, 0, n)
	{
		if (minx <= x[i] && x[i] <= maxx)
			ans++;
	}

	cout << ans;
	return 0;
}