#include <bits/stdc++.h>
#include <boost/multiprecision/cpp_int.hpp>

namespace mp = boost::multiprecision;

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;
	vector<ll> x(n), a(n);
	rep(i, 0, n)
		cin >> x[i];
	rep(i, 0, n)
		cin >> a[i];

	ll ans = 1;
	mp::cpp_int minx = x[k - 1] - a[k - 1];
	repr(i, k - 1, 0)
	{
		if (x[i - 1] < minx)
			break;
		mp::cpp_int xi = x[i];
		mp::cpp_int ai = a[i];
		if (xi - ai < minx)
			minx = xi - ai;
		ans++;
	}
	mp::cpp_int maxx = x[k - 1] + a[k - 1];
	rep(i, k - 1, n - 1)
	{
		if (maxx < x[i + 1])
			break;
		mp::cpp_int xi = x[i];
		mp::cpp_int ai = a[i];
		if (maxx < xi + ai)
			maxx = xi + ai;
		ans++;
	}

	cout << ans;
	return 0;
}