#include<bits/stdc++.h>

using namespace std;


int main(){
    int n,k = 0;
    cin >> n >> k;
    long long x[n];
    long long a[n];
    bool call[n];
    int count = 0;
    stack<long long> flog;
    for(int i = 0; i < n; i++){
        cin >> x[i];
        call[i] = false;
    }
    for(int i = 0; i < n; i++){
        cin >> a[i];
    }
    call[k-1] = true;
    flog.push(k-1);
    long long id = 0;
    while(!flog.empty()){
        id = flog.top();
        flog.pop();
        int j = 1;
        while(id + j <= n-1 && x[id]+a[id] >= x[id+j]){
            if(call[id+j] == false)flog.push(id+j);
            call[id+j] = true;
            j++;
        }
        j = 1;
        while(id-j >= 0 && x[id]-a[id] <= x[id-j]){
            if(call[id-j] == false)flog.push(id-j);
            call[id-j] = true;
            j++;
        }
    
    }
    for(int i = 0; i < n; i++){
        if(call[i]){
            count++;
        }
    }
    cout << count;
}