#include <bits/stdc++.h>

#if MYDEBUG
#include "lib/cp_debug.hpp"
#else
#define DBG(...) ;
#endif
#if __cplusplus <= 201402L
template <typename T>
T gcd(T a, T b) { return ((a % b == 0) ? b : gcd(b, a % b)); }
template <typename T>
T lcm(T a, T b) { return a / gcd(a, b) * b; }
#endif
using LL = long long;
constexpr LL LINF = 334ll << 53;
constexpr int INF = 15 << 26;
constexpr LL MOD = 1E9 + 7;

namespace Problem {
using namespace std;

class Solver2 {
 public:
  int n, k;
  vector<LL> x, a;
  Solver2(LL n, LL k) : n(n), k(k), x(n), a(n){};

  void solve() {
    for (int i = 0; i < n; ++i) {
      cin >> x[i];
    }
    for (int i = 0; i < n; ++i) {
      cin >> a[i];
    }
    int l = --k;
    LL lb = x[k] - a[k];
    while (l > 0) {
      if (x[l - 1] >= lb) {
        l--;
        lb = min(lb, x[l] - a[l]);
      } else {
        break;
      }
    }

    int r = k;
    LL rb = x[r] + a[r];
    while (r < n - 1) {
      if (x[r + 1] <= rb) {
        r++;
        rb = max(rb, x[r] + a[r]);
      } else {
        break;
      }
    }
    cout << r - l + 1 << endl;
  }
};
}  // namespace Problem

int main() {
  std::cin.tie(0);
  std::ios_base::sync_with_stdio(false);
  // std::cout << std::fixed << std::setprecision(12);
  long long n = 0, k;
  std::cin >> n >> k;

  Problem::Solver2 sol(n, k);
  sol.solve();
  return 0;
}