#include <bits/stdc++.h>
using namespace std;
long long cnt[5], ans1, ans2;
int main() {
  int n, a[200010];
  cin >> n;
  for (int i = 0; i < n; i++) {
    cin >> a[i];
    if (a[i] == 1)
      cnt[1]++;
    else
      cnt[0]++;
  }
  for (int i = 0; i < n; i++) {
    if (a[i] == 0)
      cnt[0]--;
    else {
      ans1 += cnt[0];
    }
  }
  cout << ans1;
  return 0;
}
