#include<iostream>
#include<string>
#include<iomanip>
#include<cmath>
#include<vector>
#include<algorithm>

using namespace std;

#define int long long
#define endl "\n"

const long long INF = (long long)1e18;
// const long long MOD = 1'000'000'007; 

string yn(bool f){return f?"Yes":"No";}
string YN(bool f){return f?"YES":"NO";}



signed main(){
	cin.tie(0);
	ios::sync_with_stdio(false);
	cout<<fixed<<setprecision(10);
	
	int N, K;
	vector<int> X, A;
	
	cin>>N>>K;
	
	K--;
	
	X.resize(N);
	A.resize(N);
	
	for(int i = 0; i < N; i++){
		cin>>X[i];
	}
	
	for(int i = 0; i < N; i++){
		cin>>A[i];
	}
	
	int minimum = X[K], maximum = X[K], con = 0;
	
	for(int i = K, j = K;;){
		bool flag = false;
		for(; i < N; i++){
			if(X[i] > maximum) break;
			if(maximum < X[i]+A[i]){
				maximum = X[i]+A[i];
				flag = true;
			}
			if(minimum > X[i]-A[i]){
				minimum = X[i]-A[i];
				flag = true;
			}
		}
		for(; j >= 0; j--){
			if(X[j] < minimum) break;
			if(X[j]-A[j] < minimum){
				minimum = X[j]-A[j];
				flag = true;
			}
			if(X[j]+A[j] > maximum){
				maximum = X[j]+A[j];
				flag = true;
			}
		}
		// cout<<"i = "<<i<<" j = "<<j<<" "<<minimum<<" < "<<maximum<<endl;
		if(!flag) break;
	}
	
	
	for(int i = 0; i < N; i++){
		if(minimum <= X[i] && maximum >= X[i]) con++;
	}
	
	cout<<con<<endl;
	
	return 0;
}