#pragma GCC optimize("O3") #include #define ll long long #define rep2(i,a,b) for(ll i=a;i<=b;++i) #define rep(i,n) for(ll i=0;i=b;i--) #define pii pair #define pll pair #define pq priority_queue #define pb push_back #define eb emplace_back #define veci vector #define vecll vector #define vecpii vector #define vec2(a,b) vector(a,vec(b)) #define vec2ll(a,b) vector(a,vecll(b)) #define vec3(a,b,c) vector>(a,vec2(b,c)) #define vec3ll(a,b,c) vector>(a,vec2ll(b,c)) #define fi first #define se second #define all(c) begin(c),end(c) #define ios ios_base::sync_with_stdio(0),cin.tie(0),cout.tie(0); #define lb(c,x) distance(c.begin(),lower_bound(all(c),x)) #define ub(c,x) distance(c.begin(),upper_bound(all(c),x)) using namespace std; int in() {int x;cin>>x;return x;} ll lin() {ll x;cin>>x;return x;} template inline bool chmax(T& a,T b){if(a inline bool chmin(T& a,T b){if(a>b){a=b;return 1;}return 0;} template inline void print(pair p){cout<<"("< inline void print(vector> v){for(auto e:v)print(e); cout< inline void print(T v){for(auto e:v)cout< istream& operator >> (istream& is, vector& vec){ for(T& x:vec) is >> x; return is; } const ll INF=1e9+7; int main() { ll n,k; cin >> n >> k; k--; vector a(n); ll le=0; ll ri=n-1; rep(i,n){ cin >> a[i]; if(ik && a[i]<=1){ ri=i; } } if(a[k]==0){ cout << 0 << endl; return 0; } ll ans_le=0; for(ll i=le;i<=k;i++){ ans_le+=a[i]; } ll ans_ri=0; for(ll i=k;i<=ri;i++){ ans_ri+=a[i]; } if(a[k]==1){ cout << max(ans_le,ans_ri) << endl; return 0; } else{ cout << ans_le+ans_ri-a[k] <