#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  int n, k;
  cin >> n >> k;
  k--;
  vector<int> a(n);
  for (int i = 0; i < n; i++) cin >> a[i];
  int res = 0;
  if (a[k] != 0) {
    res++;
    a[k] = 0;
  }
  for (int i = 0; i < n; i++) {
    if (i == k) continue;
    if (a[i] == 0) a[i] = n;
  }
  sort(a.begin(), a.end());
  int gap = 0;
  int ind = 0;
  int prev = 0;
  int te = n;
  for (int i = 0; i < n; i++) {
    while (ind < n && a[ind] <= i) {
      ind++;
      if (ind == n || a[ind] > i) break;
      gap += max(0, a[ind] - a[ind - 1] - 1);
    }
    ind--;
    int wrong = n - ind - 1;
    te = min(te, max(wrong, gap));
  }
  if (n > 1) res += te;
  cout << res << "\n";
  return 0;
}
