#include <iostream>
#include <cstdio>
#include <cstring>
#include <vector>
#include <deque>
#include <queue>
#include <array>
#include <set>
#include <map>
#include <cmath>
#include <algorithm>
#include <numeric>
#include <utility>
#include <tuple>
#include <functional>
#include <bitset>
#include <cstdint>
#include <cassert>
#include <random>

using namespace std;
using i64 = int64_t;
using i32 = int32_t;
template<class T, class U> void init_n(vector<T>& v, size_t n, U x) 
{ v = vector<T>(n, x); }
template<class T> void init_n(vector<T>& v, size_t n) { init_n(v, n, T()); }
template<class T> void read_n(vector<T>& v, size_t n, size_t o = 0) 
{ v = vector<T>(n+o); for (size_t i=o; i<n+o; ++i) cin >> v[i]; }
template<class T> void read_n(T a[], size_t n, size_t o = 0)
{ for (size_t i=o; i<n+o; ++i) cin >> a[i]; }
template<class T> T gabs(const T& x) { return max(x, -x); }
#define abs gabs

i64 n, k;
vector<i64> x, a;
int main() {
  cin >> n >> k;
  read_n(x, n, 1);
  read_n(a, n, 1);

  i64 i = k, j = k, l = x[k], r = x[k];
  while (true) {
    bool ex = false;
    if (i > 0 && l <= x[i]) {
      l = min(l, x[i] - a[i]);
      r = max(r, x[i] + a[i]);
      i--;
      ex = true;
    }
    if (j <= n && x[j] <= r) {
      l = min(l, x[j] - a[j]);
      r = max(r, x[j] + a[j]);
      j++;
      ex = true;
    }
    if (!ex) break;
  }
  cout << j - i - 1 << endl;
  return 0;
}