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

int main(){
    int N, K;
    cin >> N >> K;
    K--;
    int64_t X[100000], A[100000];
    for(int i=0; i<N; i++) cin >> X[i];
    for(int i=0; i<N; i++) cin >> A[i];

    int64_t L = X[K]-A[K], R = X[K]+A[K];
    int ans = 1;
    int l = K-1, r = K+1;
    while(true){
        bool updated = false;
        while(l >= 0 && L <= X[l]){
            ans++;
            updated = true;
            L = min(L, X[l]-A[l]);
            R = max(R, X[l]+A[l]);
            l--;
        }
        while(r < N && X[r] <= R){
            ans++;
            updated = true;
            L = min(L, X[r]-A[r]);
            R = max(R, X[r]+A[r]);
            r++;
        }
        if(!updated) break;
    }
    cout << ans << endl;
    return 0;
}