#include <bits/stdc++.h>

using namespace std;

#define REP(i,n) for(int i=0; i<(int)(n); i++)
#define FOR(i,b,e) for (int i=(int)(b); i<(int)(e); i++)
#define ALL(x) (x).begin(), (x).end()

const double PI = acos(-1);

int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);

  int n, k;
  cin >> n >> k;
  vector<long long> x(n), a(n);
  REP (i, n) cin >> x[i];
  REP (i, n) cin >> a[i];

  --k;

  tuple<int, int, long long, long long> p = {k, k, x[k]-a[k], x[k]+a[k]};
  bool update = true;

  while (update) {
    update = false;
    int l, r;
    long long lb, ub;
    tie(l, r, lb, ub) = p;

    if (l-1 >= 0 && lb <= x[l-1]) {
      update = true;
      --l;
      lb = min(lb, x[l] - a[l]);
      ub = max(ub, x[l] + a[l]);
    } else if (r+1 < n && x[r+1] <= ub) {
      update = true;
      ++r;
      lb = min(lb, x[r] - a[r]);
      ub = max(ub, x[r] + a[r]);
    }

    p = {l, r, lb, ub};
  }
  
  cout << (get<1>(p)- get<0>(p) + 1) << endl;
  
  return 0;
}