#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  vector<int> a(n);
  for (int i = (0); i < (n); ++i) cin >> a[i];
  long long sum = 0;
  int r = 0;
  for (int i = (0); i < (n); ++i) {
    if (a[i] == 1) {
      r++;
    } else {
      sum += r;
    }
  }
  cout << sum << endl;
  return 0;
}
