#include <bits/stdc++.h>
using namespace std;
string itosm(long long x) {
  if (x == 0) return "0";
  string res = "";
  while (x > 0) {
    res += ((x % 10) + '0');
    x /= 10;
  }
  reverse(res.begin(), res.end());
  return res;
}
long long stoim(string str) {
  long long res = 0;
  int p = 0;
  if (str[0] == '-') p++;
  for (int i = p; i < str.length(); i++) {
    res *= 10;
    res += (str[i] - '0');
  }
  return res;
}
const long long infll = 1e18 + 3;
const int inf = 1009000999;
const long double eps = 1e-7;
const int maxn = 1.5e7 + 1146;
const int baseint = 1000200013;
const long long basell = 1e18 + 3;
const long double PI = acos(-1.0);
const long long mod = 998244353;
long long binpow(long long x, long long st) {
  if (st == 0) return 1;
  if (st & 1) return binpow(x, st - 1) * x % mod;
  long long res = binpow(x, st >> 1);
  return res * res % mod;
}
int a[maxn], p[maxn];
void solve() {
  int n, d;
  cin >> n >> d;
  for (int i = 0; i < n; i++) cin >> a[i];
  for (int i = 0; i < n; i++) cin >> p[i];
  int f = a[d - 1] + p[0];
  a[d - 1] += p[0];
  int j = 1;
  for (int i = 0; i < n; i++)
    if (a[i] > f && i != d) a[i] += p[j], j++;
  for (int i = n - 1; j < n && i >= 0; i--) {
    if (i == d - 1) continue;
    a[i] += p[j];
    j++;
  }
  sort(a, a + n);
  reverse(a, a + n);
  for (int i = 0; i < n; i++)
    if (a[i] == f) {
      cout << i + 1;
      return;
    }
}
int main() {
  srand(time(0));
  ios_base::sync_with_stdio(0);
  ;
  cin.tie(0);
  cout.tie(0);
  solve();
  return 0;
}
