#include <algorithm>
#include <cfloat>
#include <climits>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <functional>
#include <iostream>
#include <map>
#include <memory>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <utility>
#include <vector>
 
using namespace std;
 
typedef long long ll;
 
#define sz size()
#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define all(c) (c).begin(), (c).end()
#define rep(i,a,b) for(ll i=(a);i<(b);++i)
#define per(i,a,b) for(ll i=b-1LL;i>=(a);--i)
#define clr(a, b) memset((a), (b) ,sizeof(a))
#define ctos(c) string(1,c)
#define print(x) cout<<#x<<" = "<<x<<endl;
 
#define MOD 1000000007

ll n,k;
vector<ll> vx,va;

ll l,r;
ll d[100100];

ll ans;

void f(ll p){
	if(d[p]==0&&l<=vx[p]&&vx[p]<=r){
		ans++;
		d[p]=1;
		l = min(l,vx[p]-va[p]);
		r = max(r,vx[p]+va[p]);
		if(p<n-1)f(p+1);
		if(0<p)f(p-1);
	}
}

int main() {
	clr(d,0);
	ans = 0;
	cin>>n>>k;
	k--;
	rep(i,0,n){
		ll a;
		cin>>a;
		vx.pb(a);
	}
	rep(i,0,n){
		ll a;
		cin>>a;
		va.pb(a);
	}
	l = vx[k];
	r = vx[k];
	f(k);
	cout << ans << endl;
	return 0;
}