#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, a, i, j, arr[300] = {0}, p = 0, k = 0, c, d;
  cin >> n >> a;
  for (i = 1; i < n + 1; i++) {
    cin >> arr[i];
  }
  arr[0] = 1, arr[n + 1] = 1;
  j = min(a, n - a + 1);
  for (i = j; i < n + 1; i++) {
    c = a + k;
    d = a - k;
    if (d < 1) d = 0;
    if (c > n) c = n + 1;
    if (arr[d] == arr[c] and arr[c]) {
      if (c != d and c <= n and d > 0)
        p += 2;
      else
        p++;
    }
    k++;
  }
  cout << p << endl;
  return 0;
}
