#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define llong long long

int main() {
    int n, k;
    cin >> n >> k;
    vector<llong> x(n);
    rep(i, n) cin >> x[i]; 
    vector<llong> a(n);
    rep(i, n) cin >> a[i]; 

    bool left = true;
    bool right = true;
    int count = 1;
    llong left_val = x[k-1] - a[k-1];
    llong right_val = x[k-1] + a[k-1];
    int left_idx = k-1;
    int right_idx = k-1;
    while (left || right) {
        while (left && left_idx-1 >= 0) {
            if(x[left_idx-1] < left_val) {
                left = false;
            } else {
                left_idx -= 1;
                left_val = min(left_val, x[left_idx] - a[left_idx]);
                right_val = max(right_val, x[left_idx] + a[left_idx]);
                if(right_val == x[left_idx] + a[left_idx]) right = true;
                count += 1;
            }
        }
        left = false;
        while (right && right_idx+1 < n) {
            if(x[right_idx+1] > right_val) {
                right = false;
            } else {
                right_idx += 1;
                right_val = max(right_val, x[right_idx] + a[right_idx]);
                left_val = min(left_val, x[right_idx] - a[right_idx]);
                if(left_val == x[right_idx] - a[right_idx]) left = true;
                count += 1;
            }
        }
        right = false;
    }
    cout << count << endl;
}