#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define P pair<ll,ll>
#define FOR(I,A,B) for(ll I = ll(A); I < ll(B); ++I)
#define FORR(I,A,B) for(ll I = ll((B)-1); I >= ll(A); --I)
#define TO(x,t,f) ((x)?(t):(f))
#define SORT(x) (sort(x.begin(),x.end())) // 0 2 2 3 4 5 8 9
#define POSL(x,v) (lower_bound(x.begin(),x.end(),v)-x.begin()) //xi>=v  x is sorted
#define POSU(x,v) (upper_bound(x.begin(),x.end(),v)-x.begin()) //xi>v  x is sorted
#define NUM(x,v) (POSU(x,v)-POSL(x,v))  //x is sorted
#define REV(x) (reverse(x.begin(),x.end())) //reverse
ll gcd(ll a,ll b){if(a%b==0)return b;return gcd(b,a%b);}
ll lcm(ll a,ll b){ll c=gcd(a,b);return ((a/c)*(b/c)*c);}
#define NEXTP(x) next_permutation(x.begin(),x.end())
const ll INF=ll(1e18)+ll(7);
const ll MOD=1000000007LL;
#define out(a) cout<<fixed<<setprecision((a))




int main(){
	ll N,K;
	cin >> N >> K;
	K--;
	vector<ll> X(N),A(N);
	FOR(i,0,N)cin>>X[i];
	FOR(i,0,N)cin>>A[i];
	ll L=K,R=K;
	FOR(i,K,N){
		if(i<=R){
			ll B = POSU(X,X[i]+A[i]) - 1;
			R = max(R,B);
		}
	}
	FORR(i,0,K+1){
		if(i>=L){
			ll B = POSL(X,X[i]-A[i]);
			L = min(L,B);
		}
	}
	cout << R-L+1 << endl;
}