#include "bits/stdc++.h"

using namespace std;
#ifdef _DEBUG
#define _GLIBCXX_DEBUG
#include "dump.hpp"
#else
#define dump(...)
#endif

#define int long long
#define ll long long
#define DBG 1
#define rep(i, a, b) for (int i = (a); i < (b); i++)
#define rrep(i, a, b) for (int i = (b)-1; i >= (a); i--)
#define loop(n) rep(loop, (0), (n))
#define all(c) begin(c), end(c)
const int INF = sizeof(int) == sizeof(long long) ? 0x3f3f3f3f3f3f3f3fLL : 0x3f3f3f3f;
const int MOD = (int)(1e9) + 7;
#define fi first
#define se second
#define pb push_back
#define eb emplace_back
using pii = pair<int, int>;
// template<class T> ostream &operator<<(ostream &os,T &t){dump(t);return os;}
template <typename T, typename S>istream &operator>>(istream &is, pair<T, S> &p) { is >> p.first >> p.second; return is; }
//template <typename T, typename S>ostream &operator<<(ostream &os, pair<T, S> &p) {os << p.first << " " << p.second;return os;}

template <typename T> void printvv(const vector<vector<T>> &v) {
	cerr << endl;
	rep(i, 0, v.size()) rep(j, 0, v[i].size()) {
		if (typeid(v[i][j]).name() == typeid(INF).name() and v[i][j] == INF) {
			cerr << "INF";
		}
		else
			cerr << v[i][j];
		cerr << (j == v[i].size() - 1 ? '\n' : ' ');
	}
	cerr << endl;
}

#ifndef _DEBUG
#define printvv(...)
#endif
void YES(bool f) { cout << (f ? "YES" : "NO") << endl; }
void Yes(bool f) { cout << (f ? "Yes" : "No") << endl; }
template <class T, class U>bool chmin(T& a, U b) { if (a > b) { a = b; return true; }return false; }
template <class T, class U>bool chmax(T& a, U b) { if (a < b) { a = b; return true; }return false; }

signed main(signed argc, char *argv[]) {
	cin.tie(0);
	ios::sync_with_stdio(false);
	cout << fixed << setprecision(12);

	int N, K; cin >> N >> K;
	vector<int>X(N); rep(i, 0, N) { cin >> X[i]; }
	vector<int>A(N); rep(i, 0, N) { cin >> A[i]; }

	K--;
	vector<int>visited(N);
	visited[K] = 1;
	queue<int>q;
	q.push(K);
	int l = X[K], r = X[K];
	int il = K, ir = K;
	while (q.size()) {
		int v = q.front(); q.pop();
		chmin(l, X[v] - A[v]);
		chmax(r, X[v] + A[v]);
		if (il - 1 >= 0 and not visited[il - 1] and l <= X[il - 1]) {
			visited[il - 1] = 1;
			q.push(il - 1);
			il--;
		}
		if (ir + 1 < N and not visited[ir + 1] and X[ir + 1] <= r) {
			visited[ir + 1] = 1;
			q.push(ir + 1);
			ir++;
		}
	}
	cout << count(all(visited), 1) << endl;

	return 0;
}