D. Kozak Vus and the Array

Cossack Vus recently discovered an array $a$ with $n$ elements, where each element is either a zero or a one.

He is curious to know: what is the minimum number of swaps between adjacent elements required to sort this array?

Input

The first line contains a single integer $n$ ($1\le n\le 10^6$) — the length of the array $a$.

The second line contains $n$ integers $a_1,a_2,\dots ,a_n$ ($0\le a_i\le 1$) — the elements of the array $a$.

Output

Print a single integer — the minimum number of adjacent swaps needed to sort the array.

Examples

Scoring

If your solution works correctly for $n\le 1,000$, it will earn at least $35$ points.