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

int main() {
  int n, k;
  cin >> n >> k;
  k--;
  vector<int> a(n);
  for(int i = 0; i < n; i++) cin >> a[i];
  if(a[k] == 0) {
    cout << 0 << endl;
    return 0;
  }
  long long ans = a[k];
  int pos = k;
  while(pos && a[pos - 1]) {
    pos--;
    ans += a[pos];
    if(a[pos] == 1) break;
  }
  pos = k;
  while(pos < n - 1 && a[pos + 1]) {
    pos++;
    ans += a[pos];
    if(a[pos] == 1) break;
  }
  cout << ans << endl;
}