#include <bits/stdc++.h>
using namespace std;
int arr[200000], arr2[200000];
int main() {
  int n, i;
  long long sum = 0;
  scanf("%d", &n);
  for (i = 0; i < n; i++) {
    scanf("%d", &arr[i]);
    arr2[i] = arr[i] + arr2[i - 1];
  }
  for (i = 0; i < n; i++) {
    if (arr[i] == 0) {
      sum += arr2[i];
    }
  }
  cout << sum;
  return 0;
}
