#include <bits/stdc++.h>
using namespace std;
 
#define REP(i, s) for (int i = 0; i < s; ++i)
#define ALL(v) (v).begin(), (v).end()
#define COUT(x) cout << #x << " = " << (x) << " (L" << __LINE__ << ")" << endl
#define EACH(i, s) for (__typeof__((s).begin()) i = (s).begin(); i != (s).end(); ++i)
#define DEBUG
#define int long long
#define INF 1e18
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
template<class T1, class T2> ostream& operator << (ostream &s, pair<T1,T2> P)
{ return s << '<' << P.first << ", " << P.second << '>'; }
template<class T> ostream& operator << (ostream &s, vector<T> P)
{ for (int i = 0; i < P.size(); ++i) { if (i > 0) { s << " "; } s << P[i]; } return s; }
template<class T> ostream& operator << (ostream &s, vector<vector<T> > P)
{ for (int i = 0; i < P.size(); ++i) { s << endl << P[i]; } return s << endl; }
template<class T> ostream& operator << (ostream &s, set<T> P)
{ EACH(it, P) { s << "<" << *it << "> "; } return s << endl; }
template<class T1, class T2> ostream& operator << (ostream &s, map<T1,T2> P)
{ EACH(it, P) { s << "<" << it->first << "->" << it->second << "> "; } return s << endl; }
template<class T>void show(vector<T>v){for (int i = 0; i < v.size(); i++){cerr<<v[i]<<" ";}cerr<<"\n";}
typedef long long ll;

signed main()
{
    int n,k;
    cin>>n>>k;
    k--;
    vector<int>a(n);
    REP(i,n) cin>>a[i];
    int index1=0;
    if(k-1>=0){
    for (size_t i = k-1; i>=0; i--)
    {
        if(a[i]==0){
            index1=i+1;
            break;
        }
        if(a[i]==1){
            index1=i;
            break;
        }
    }
    }
    int index2=n-1;
    if(k+1<n){
    for (size_t i = k + 1; i < n; i++)
    {
        if (a[i] == 0)
        {
            index2 = i - 1;
            break;
        }
        if (a[i] == 1)
        {
            index2 = i;
            break;
        }
    }
    }
    if(a[k]==0){
        cout<<0<<endl;
    }
    else{
    int cnt1=0,cnt2=0;
    if(k-1>=0){
    for (size_t i = k-1; i >=index1; i--)
    {
        cnt1+=a[i];
     //   cerr<<a[i]<<endl;
    }
    }
    if(k+1<n){
    for (int i = k+1; i <=index2 ; i++)
    {
        cnt2+=a[i];
    }
    }
    if(a[k]==1){
        cout<<a[k]+max(cnt1,cnt2)<<endl;
    }
    else{
        cout<<a[k]+cnt1+cnt2<<endl;
    }
   // cerr<<cnt1<<" "<<cnt2<<endl;
    }
    return 0;
}