#include <bits/stdc++.h>
using namespace std;
using Int = long long;
template<typename T1,typename T2> inline void chmin(T1 &a,T2 b){if(a>b) a=b;}
template<typename T1,typename T2> inline void chmax(T1 &a,T2 b){if(a<b) a=b;}


template<typename T> void drop(const T &x){cout<<x<<endl;exit(0);}

//INSERT ABOVE HERE
signed main(){
  cin.tie(0);
  ios::sync_with_stdio(0);

  Int n,k;
  cin>>n>>k;
  k--;
  vector<Int> as(n);
  for(Int i=0;i<n;i++) cin>>as[i];
  if(as[k]==0) drop(0);

  Int l=0,r=0;
  for(Int i=k-1;i>=0;i--){
    if(as[i]==0) break;
    l+=as[i];
    if(as[i]==1) break;
  }

  for(Int i=k+1;i<n;i++){
    if(as[i]==0) break;
    r+=as[i];
    if(as[i]==1) break;
  }

  if(as[k]==1) cout<<max(l,r)+1<<endl;
  else cout<<l+r+as[k]<<endl;
  return 0;
}