#include <iostream>
using namespace std;
typedef long long ll;

int main()
{
    int n;
    cin >> n;
    int a[200005];
    for(int i = 0; i < n; i++) cin >> a[i];
    a[n] = 0;
    ll s[200005];
    s[n - 1] = 0;
    for(int i = n - 2; i >= 0; i--){
        if(a[i] == 0) s[i] = 0;
        if(a[i] == 1){
            if(i < n - 2 && a[i + 1] == 0){
                if(a[i + 2] == 1) s[i] = s[i + 2] + 2;
                else s[i] = 2;
            }
            else s[i] = 1;
        }
    }
    ll ans = 0;
    for(int i = 0; i < n; i++) ans += s[i];
    cout << ans << endl;
}