#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  vector<int> g;
  while (cin >> n) {
    int xi, xf;
    xi = -1;
    xf = -1;
    bool init = false;
    g = vector<int>(n);
    for (int i = 0; i < n; i++) {
      cin >> g[i];
      if (init == false && g[i] == 1) {
        xi = i;
        xf = i;
        init = true;
      } else if (init == true && g[i] == 1)
        xf = max(xf, i);
    }
    if (xi == -1 || xf == -1)
      cout << 0 << endl;
    else {
      int ceros = 0;
      for (int i = xi; i < xf;) {
        if (g[i] == 0 && g[i + 1] == 0) {
          i += 2;
          ceros += 2;
          int b = i;
          for (int q = b; q <= xf; q++)
            if (g[q] == 0) {
              ceros++;
              b = max(b, q);
            } else
              break;
          i = b + 1;
        } else
          i++;
      }
      cout << (xf - xi + 1) - ceros << endl;
    }
  }
  return 0;
}
