#include <bits/stdc++.h>
using namespace std;

int main()
{
    int N, K;
    cin >> N >> K;
    vector<int> A(N);
    for (int i = 0; i < N; i++)
    {
        cin >> A[i];
    }
    K--;
    long long left = 0;
    long long right = 0;
    for (int i = K + 1; i < N; i++)
    {
        if (A[i] == 0)
        {
            break;
        }
        right += A[i];
        if (A[i] == 1)
        {
            break;
        }
    }
    for (int i = K - 1; i >= 0; i--)
    {
        if (A[i] == 0)
        {
            break;
        }
        left += A[i];
        if (A[i] == 1)
        {
            break;
        }
    }
    if (A[K] == 0)
    {
        cout << 0;
        return 0;
    }
    else if (A[K] == 1)
    {
        cout << max(left, right);
    }
    else
    {
        cout << left + right;
    }
}