#include <bits/stdc++.h>
using namespace std;

int main() {
  long N, K;
  cin >> N >> K;
  K--;
  vector<long> X(N), A(N);
  for (long i = 0; i < N; i++) cin >> X.at(i);
  for (long i = 0; i < N; i++) cin >> A.at(i);
  long L = X.at(K) - A.at(K);
  long R = X.at(K) + A.at(K);
  long l = K, r = K;
  long cnt = 1e6;
  while (cnt--) {
    l--;
    if (l < 0) l++;
    else {
      if (X.at(l) < L) l++;
      else {
        L = min(L, X.at(l) - A.at(l));
        R = max(R, X.at(l) + A.at(l));
      }
    }
    r++;
    if (r >= N) r--;
    else {
      if (X.at(r) > R) r--;
      else {
        R = max(R, X.at(r) + A.at(r));
        L = min(L, X.at(r) - A.at(r));
      }
    }
  }
  cout << r - l + 1 << "\n";
}