#define _GLIBCXX_DEBUG
#include <bits/stdc++.h>
#include <atcoder/dsu>
#include <atcoder/segtree>
using namespace atcoder;
using namespace std;
typedef long long ll;
#define rep(i,a,b) for(int i=a;i<b;i++)
using vi = vector<int>; 
using vvi = vector<vi>; 
using li =vector<ll>;
using lli=vector<li>;
using si =vector<char>;
using ssi =vector<si>;
const long long INF = 1e18;
const long long MOD=1e9+7;
//for (auto [key, val] : mp)
int main() { ll n,k;cin>>n>>k;
li vec(n);
rep(i,0,n)cin>>vec[i];
ll a=0,b=n-1;
rep(i,0,k-1){if(vec[i]==1){a=i;}if(vec[i]==0){a=i+1;}}
rep(i,k,n){if(vec[i]==1){b=i;break;}else if(vec[i]==0){b=i-1;break;}}
if(vec[k-1]>1){
	ll ans=0;
	rep(i,a,b+1)ans+=vec[i];
cout<<ans;
}
else if(vec[k-1]==1) {
	ll ans=0;
	rep(i,a,k-1)ans+=vec[i];
	ll B=0;
	rep(i,k,b)B+=vec[i];
	if(B<ans)cout<<ans;
	else cout<<B;
}
else cout<<0;
}