#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
typedef pair<long long,long long> pll;
#define pb push_back
#define mp make_pair
#define rep(i,n) for(int i=0;i<(n);++i)
constexpr int mod=1000000007;
constexpr int mod1=998244353;
vector<int> dx={0,-1,0,1},dy={1,0,-1,0};
bool inside(int y,int x,int h,int w){
	if(y<h && y>=0 && x<w && x>=0) return true;
	return false;
}





int main(){
	cin.tie(0);
	ios::sync_with_stdio(false);
	int n, k;cin >> n >> k;
	k--;
	vector<ll> x(n), a(n);
	rep(i,n) cin >> x.at(i);
	rep(i,n) cin >> a.at(i);
	ll l = x.at(k) - a.at(k), r = x.at(k) + a.at(k), L = k - 1, R = k + 1, ans = 1;
	while(true){
		bool flg = true;
		if(L >= 0 && x.at(L) >= l){
			l = min(l, x.at(L) - a.at(L));
			r = max(r, x.at(L) + a.at(L));
			L--;
			ans++;
			flg = false;
		}
		if(R < n && x.at(R) <= r){
			r = max(r, x.at(R) + a.at(R));
			l = min(l, x.at(R) - a.at(R));
			R++;
			ans++;
			flg = false;
		}
		if(flg) break;
	}
	cout << ans << endl;
}