#include <iostream>
#include <vector>
#include <algorithm>
#include <functional>
#include <queue>
#include <map>
#include <cmath>
#include <iomanip>
#include <set>

using namespace std;

int main() {
  int n , k;
  cin >> n >> k;
  k--;
  vector<long long> X(n);
  for (int i = 0; i < n; i++) {
    cin >> X[i];
  }
  vector<long long> A(n);
  for (int i = 0; i < n; i++) {
    cin >> A[i];
  }

  int x = k , y = k;
  int ans = 0;
  long long mx = -1e18;
  long long mn = 1e18;
  queue<int> qx , qy;
  qx.push(k);
  qy.push(k);
  while (qx.size() > 0 || qy.size() > 0) {
    x = qx.front();
    qx.pop();
    mx = max(mx , X[x] + A[x]);
    if (x + 1 < n && X[x + 1] <= mx) {
      qx.push(x + 1);
    }
    y = qy.front();
    qy.pop();
    mn = min(mn , X[y] - A[y]);
    if (0 <= y - 1 && mn <= X[y - 1]) {
      qy.push(y - 1);
    }
  }
  cout << x - y + 1 << endl;
  return 0;
}