#include <bits/stdc++.h>
using namespace std;
long long arr[1000000], arr1[1000000], cnt2[1000000];
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  long long n, k, i, j, x, y, z, ans, a, b, c;
  cin >> n >> k;
  for (i = 1; i <= n; i++) {
    cin >> arr[i];
  }
  for (i = 1; i <= n; i++) {
    cin >> arr1[i];
  }
  x = arr[k] + arr1[1];
  y = 1;
  z = n;
  for (i = 1; i <= k; i++) {
    if (arr[i] + arr1[z] <= x) {
      z--;
    } else if (arr[i] + arr1[z] > x) {
      y++;
    }
  }
  cout << y << endl;
}
