#include<iostream>
#include<string>
#include<cstdio>
#include<vector>
#include<cmath>
#include<algorithm>
#include<functional>
#include<iomanip>
#include<queue>
#include<ciso646>
#include<random>
#include<map>
#include<set>
#include<bitset>
#include<stack>
#include<unordered_map>
#include<utility>
#include<cassert>
using namespace std;

//#define int long long
typedef long long ll;

typedef unsigned long long ul;
typedef unsigned int ui;
const ll mod = 1000000007;
const ll INF = mod * mod;
typedef pair<int, int> P;
#define stop char nyaa;cin>>nyaa;
#define rep(i,n) for(int i=0;i<n;i++)
#define per(i,n) for(int i=n-1;i>=0;i--)
#define Rep(i,sta,n) for(int i=sta;i<n;i++)
#define rep1(i,n) for(int i=1;i<=n;i++)
#define per1(i,n) for(int i=n;i>=1;i--)
#define Rep1(i,sta,n) for(int i=sta;i<=n;i++)
typedef pair<ll, ll> LP;
typedef vector<ll> vec;
typedef long double ld;
typedef pair<ld, ld> LDP;
const ld eps = 1e-5;


void solve() {
	int n, k; cin >> n >> k;
	vector<ll> x(n);
	vector<ll> a(n);
	rep(i, n) {
		cin >> x[i];
	}
	rep(i, n) {
		cin >> a[i];
	}
	k--; ll le = x[k] - a[k]; ll ri = x[k] + a[k];
	int l = k - 1; int r = k + 1;
	while (true) {
		if (l >= 0 && x[l] >= le) {
			le = min(le, x[l] - a[l]);
			ri = max(ri, x[l] + a[l]);
			l--; continue;
		}
		if (r < n&&x[r] <= ri) {
			le = min(le, x[r] - a[r]);
			ri = max(ri, x[r] + a[r]);
			r++; continue;
		}


		break;
	}
	cout << (r - l - 1) << endl;
}

signed main() {
	ios::sync_with_stdio(false);
	cin.tie(0);
	//cout << fixed << setprecision(5);
	//init();
	solve();

	//cout << "finish" << endl;
	//stop
	return 0;
}