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

int n, m;
bool a[200000];
int b[200000];

int main(){
    cin >> n;
    
    for(int i = 0; i < n; i++)
        cin >> a[i];
    
    for(int i = n - 2; i >= 0; i--){
        if(a[i]){
            bool f = 0;
            int j = i + 1;
            b[i]++;
            
            while(j < n - 1 && a[j] == f){
                if(b[j] > 0){
                    b[i] += b[j];
                    break;
                }
                
                b[i]++;
                f = !f;
                j++;
            }
                        
            m += b[i];
        }
    }
    
    cout << m << endl;
}