#include <bits/stdc++.h>
using namespace std;

#define FOR(i, m, n) for(int (i) = (m); (i) < (n); (i)++)
#define rep(i, n) FOR(i, 0, n)
#define repn(i, n) FOR(i, 1, n+1)
#define co(n) cout << (n) << endl
#define cosp(n) cout << (n) << ' '
#define setp(n) cout << fixed << setprecision(n);
#define all(s) (s).begin(), (s).end()
#define pb push_back
#define mp make_pair
#define fs first
#define sc second
typedef long long ll;
typedef pair<int, int> P;

const ll INF = 1e9+1;
const ll LINF = 1e18+1;
const ll MOD = 1e9+7;
//const ll MOD = 998244353;
const double PI = acos(-1);
const double EPS = 1e-9;

int main(void){
	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];

	int ans = 1, left = k-2, right = k;
	ll left_x = x[k-1]-a[k-1], right_x = x[k-1]+a[k-1];
	while((x[left] >= left_x || x[right] <= right_x) && ans < n){
		if(left >= 0 && x[left] >= left_x){
			left_x = min(left_x, x[left]-a[left]);
			right_x = max(right_x, x[left]+a[left]);
			ans++;
			left--;
		}
		if(right < n && x[right] <= right_x){
			left_x = min(left_x, x[right]-a[right]);
			right_x = max(right_x, x[right]+a[right]);
			ans++;
			right++;
		}
	}

	co(ans);

	return 0;
}