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

long long n, k, i, j;

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