#include <iostream>
#include <algorithm>
using namespace std;

int n, k, i, j;

int main(){
    cin >> n >> k;
    int p, q;
    int a[n];
    int ans = 0;
    int tmp = 0, tmpa = 0, tmpb = 0;
    for(i = 0; i < n; i++){cin >> a[i];}
    
    if(a[k - 1] == 0){ 
        cout << 0 << endl;
        return 0;
    }
    
    p = 0, q = n - 1;
    if(a[k - 1] == 1) tmp = 1;
    for(i = 0; i < n; i++){
        if(i < k - 1){
            if(a[i] == 0) p = i + 1;
            if(a[i] == 1) p = i;
        }else if(i > k - 1){
            if(a[i] == 0) {q = i - 1; break;}
            if(a[i] == 1) {q = i; break;}
            
        }                
    }
    
    for(i = p; i < q + 1; i++){
        if(tmp == 0) ans += a[i];
        else{
            if(i < k) tmpa += a[i];
            if(i >= k - 1) tmpb += a[i];
        }
    }
    
    if(tmp == 1) ans = max(tmpa, tmpb);
    
    cout << ans << endl;
    
    return 0;
}