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

#define ll long long
#define rep(i, n) for (int i = 0; i < (n); i++)
#define P pair<int, int>

int main() {
  int n;
  cin >> n;
  vector<int> a(n);
  rep(i,n) cin >> a[i];
  vector<int> nxt(n);
  if (a[n-1] == 0) nxt[n-1] = n-1;
  else nxt[n-1] = n;
  for (int i = n-2; i >= 0; i--) {
    if (a[i] == 0) nxt[i] = i;
    else nxt[i] = nxt[i+1];
  }
  ll ans = 0;
  rep(i,n) ans += (ll)n-nxt[i];
  cout << ans << endl;


}