typedef long long ll;
typedef long double ld;
#include <bits/stdc++.h>
using namespace std;
#define int long long

signed main(){
    ll n;
    std::cin >> n;
    vector<ll> a(n),b(n);
    for (int i = 0; i < n; i++) {
        std::cin >> a[i];
        b[i] = a[i];
        if(i%2==1){
            b[i] = !b[i];
        }
    }
    vector<ll> zi,oi;
    for (int i = 0; i < n; i++) {
        if(b[i]){
            oi.push_back(i);
        }else{
            zi.push_back(i);
        }
        // std::cout << b[i]<<" ";
    }
    // std::cout << std::endl;
    ll ans = 0;
    for (int i = 0; i < n; i++) {
        if(a[i]==1){
            auto &c = (b[i]? zi : oi);
            // std::cout << "c: "<<c.size() << std::endl;
            auto it = lower_bound(c.begin(),c.end(),i+1);
            if(it==c.end()){
                ans += n-i-1;
            }else{
                // std::cout << i<<" "<<*it << std::endl;
                ans += *it-i;
            }
        }
        // std::cout << ans << std::endl;
    }
    std::cout << ans << std::endl;
}