#include <bits/stdc++.h>
using namespace std;
const int inf = 1e9 + 1;
const int N = 200123;
int z, n, s;
deque<int> dq;
int t[N];
int main() {
  ios_base::sync_with_stdio(0);
  int ans = 0;
  cin >> n >> s;
  for (int i = 0; i < n; i++) {
    cin >> t[i];
    if (i + 1 == s) {
      ans += (t[i] != 0);
      n--;
      i--;
      s = inf;
    } else if (t[i] == 0)
      t[i] = n + 5;
  }
  sort(t, t + n);
  for (int i = 0; i < n; i++) {
    dq.push_back(t[i]);
  }
  int nxt = 1;
  while (dq.size()) {
    while (dq.size() && nxt < dq.front()) {
      dq.pop_back();
      nxt++;
      ans++;
    }
    if (dq.size()) {
      nxt = max(nxt, dq.front() + 1);
      dq.pop_front();
    }
  }
  cout << ans << endl;
}
