#include <bits/stdc++.h>
using namespace std;
int main() {
  long long int i, j, k, l = 0, n, m = 0;
  cin >> n;
  int a[n];
  for (i = 0; i < n; i++) {
    cin >> a[i];
    if (a[i] == 1)
      l++;
    else
      m += l;
  }
  cout << m;
}
