#include <bits/stdc++.h>
using namespace std;
const double pi = 3.14159265358979323846;
const double E = 2.7182818284590452354;
const struct _ {
  ios_base::Init i;
  _() {
    srand(time(NULL));
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
  }
} _;
template <class I>
inline void in(I A, I B) {
  while (A != B) {
    cin >> *A;
    ++A;
  }
}
template <class I>
inline void out(I A, I B, char D = ' ') {
  if (A != B) {
    cout << *A;
    while (++A != B) {
      cout << D << *A;
    }
  }
  cout << '\n';
}
template <class T>
inline T sq(const T& X) {
  return X * X;
}
template <class T>
inline T power(T X, int Y) {
  assert(Y >= 0 && !(X == 0 && Y == 0));
  T R = (Y & 1) ? X : 1;
  while (Y >>= 1) {
    X *= X;
    if (Y & 1) R *= X;
  }
  return R;
}
int main() {
  int n;
  cin >> n;
  long long res = 0, acc = 0;
  while (n--) {
    int a;
    cin >> a;
    if (a == 1) {
      acc++;
    } else {
      res += acc;
    }
  }
  cout << res << '\n';
}
