#include <bits/stdc++.h>
using namespace std;
int a[200002], b[200002];
int main() {
  int n, i, j, d, s = 1, u;
  cin >> n >> d;
  for (i = 1; i <= n; i++) cin >> a[i];
  cin >> u;
  a[d] += u;
  u = 0;
  for (i = 1; i < n; i++) cin >> b[i];
  for (i = 1, j = n - 1; i <= n && j > 0; i++) {
    if (i == d) continue;
    if (a[i] + b[j] > a[d]) {
      if (u)
        u--;
      else
        s++;
    } else {
      while (j > 0 && a[i] + b[j] <= a[d]) u++, j--;
      u--;
    }
  }
  cout << s;
}
