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

int main()
{
    int N;
    cin >> N;
    vector<int> A(N);
    vector<int> zero;
    for (int i = 0; i < N; i++)
    {
        cin >> A[i];
        if (A[i] == 0)
        {
            zero.push_back(i);
        }
    }
    long long ans = 0;
    for (int i = 0; i < N; i++)
    {
        auto it = lower_bound(zero.begin(), zero.end(), i);
        if (it != zero.end())
        {
            int r = *it;
            ans += N - r;
        }
    }
    cout << ans;
}