#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i = 0; i < (n);i++)
#define sz(x) int(x.size())
typedef long long ll;
typedef pair<int,int> P;
constexpr int INF = 1e9;

template <typename T> 
struct SegmentTree {
  
  int n;
  vector<T> node;

  T f(T a, T b) {return (a + b);}

  SegmentTree (int sz, T init = 0) {
    n = 1; while (n < sz) n <<= 1;
    node.assign(2*n, init);
  }

  void update(int k, T x) {
    k += (n - 1);
    node[k] = x;
    while (k > 0) {
      k = (k - 1) >> 1;
      node[k] = f(node[2*k+1], node[2*k+2]);
    } 
  }

  T query(int a, int b, int k = 0, int l = 0, int r = -1) {
    if (r < 0) r = n;
    if (r <= a || b <= l) return 0;
    if (a <= l && r <= b) return node[k];
    T vl = query(a, b, 2*k+1, l, (l+r)/2);
    T vr = query(a, b, 2*k+2, (l+r)/2, r);
    return f(vl, vr);
  }

  T getvalue(int k) {
    return query(k,k+1);
  }

};

int main(){
  int n, k;
  cin >> n >> k;
  k--;
  vector<int> a(n);
  rep(i,n) cin >> a[i];
  vector<int> l(n, 0), r(n, n-1);
  SegmentTree<ll> seg(n);

  int prev = 0;
  for (int i = 0; i < n; i++) {
    l[i] = prev;
    seg.update(i,a[i]);
    if (a[i] == 1 || a[i] == 0) prev = i;
  }
  prev = n-1;
  for (int i = n-1; i >= 0; i--) {
    r[i] = prev;
    if (a[i] == 1 || a[i] == 0) prev = i;
  }
  if (a[k] == 0) {
    cout << 0 << endl;
    return 0;
  }
  if (a[k] == 1) {
    cout << max(seg.query(l[k], k + 1), seg.query(k, r[k] + 1)) << endl;
    return 0;
  }
  
  cout << seg.query(l[k], k) + seg.query(k, r[k] + 1) << endl;

  return 0;
}