#include <bits/stdc++.h> using namespace std; typedef long long ll; #define pb push_back #define fi first #define se second typedef pair<ll,ll> P; using VP = vector<P>; using VVP = vector<VP>; using VI = vector<ll>; using VVI = vector<VI>; using VVVI = vector<VVI>; const int inf=1e9+7; const ll INF=1LL<<61; const ll mod=1e9+7; template<class T> inline bool chmax(T &a, T b) { if(a < b) { a = b; return true; } return false; } template<class T> inline bool chmin(T &a, T b) { if(a > b) { a = b; return true; } return false; } int main(){ int i,j; ll n,k; cin>>n>>k; ll a[n+1]; ll ans=0; for(i=1;i<=n;i++) cin>>a[i]; if(a[k]==0){ cout<<0<<endl; return 0; } if(a[k]==1){ ll ans=0; ll cnt=0; for(i=k+1;i<=n;i++){ if(a[i]>=2) cnt+=a[i]; else { cnt+=a[i]; break; } } ans=max(ans,1+cnt); cnt=0; for(i=k-1;i>=1;i--){ if(a[i]>=2) cnt+=a[i]; else { cnt+=a[i]; break; } } ans=max(ans,1+cnt); cout<<ans<<endl; return 0; } else{ ll ans=0; ll cnt=0; for(i=k+1;i<=n;i++){ if(a[i]>=2) cnt+=a[i]; else { cnt+=a[i]; break; } } for(i=k-1;i>=1;i--){ if(a[i]>=2) cnt+=a[i]; else { cnt+=a[i]; break; } } ans=max(ans,a[k]+cnt); cout<<ans<<endl; return 0; } }