#include <bits/stdc++.h>
using namespace std;
inline long long read() {
  long long x = 0;
  char ch = getchar();
  bool f = 0;
  for (; !isdigit(ch); ch = getchar())
    if (ch == '-') f = 1;
  for (; isdigit(ch); ch = getchar()) x = x * 10 + ch - '0';
  return f ? -x : x;
}
void write(long long x) {
  if (x < 0) putchar('-'), x = -x;
  if (x >= 10) write(x / 10);
  putchar(x % 10 + '0');
}
void writeln(long long x) {
  write(x);
  puts("");
}
void writep(long long x) {
  write(x);
  putchar(' ');
}
const int N = 2e5 + 5;
int n, cnt;
long long ans;
int main() {
  n = read();
  for (int i = (int)(1); i <= (int)(n); i++) {
    int x = read();
    if (x)
      cnt++;
    else
      ans += cnt;
  }
  cout << ans;
}
