#include<iostream>
#include<vector>
signed main(){
  int n,k;
  std::cin>>n>>k;
  k--;
  std::vector<int> a(n);
  for(auto& ai:a)std::cin>>ai;
  int l=k,r=k;
  while(l>0){
    if(a[l]<=1)break;
    l--;
  }
  while(r<n){
    if(a[r]<=1)break;
    r++;
  }
  if(a[k]==1){
    int64_t suml=0,sumr=0;
    for(int i=k;i>=l;--i)suml+=a[i];
    for(int i=k;i<=r;++i)sumr+=a[i];
    std::cout<< std::max(suml,sumr) <<std::endl;
    return 0;
  }
  int64_t ans = 0;
  for(int i=l;i<=r;++i)ans+=a[i];
  std::cout<< ans <<std::endl;
}