#include <bits/stdc++.h>
using namespace std;
int n, s, a[200100], cnt[200100], ans, kol;
set<int> st;
int main() {
  cin >> n >> s;
  for (int i = 1; i <= n; ++i) {
    cin >> a[i];
  }
  for (int i = 1; i <= n; ++i) {
    if (i == s) {
      if (a[i] != 0) {
        a[i] = 0;
        ans++;
      }
      st.insert(a[i]);
      continue;
    }
    if (a[i] == 0) {
      a[i] = n;
      kol++;
    }
    cnt[a[i]]++;
    st.insert(a[i]);
  }
  for (int i = 1; i <= n; ++i) {
    if (i > *st.rbegin()) break;
    if (cnt[i] == 0) {
      int pp = *st.rbegin();
      if (cnt[pp] == 1) {
        st.erase(pp);
      }
      ans++;
      st.insert(i);
      cnt[pp]--;
    }
  }
  cout << max(ans, kol);
}
