## Goal

Given a list of 1 and 0, you must regroup all the 1 at the begin of the list in a minimum number of steps. A step is the interchange of two elements located at different positions.

The expected result is the minimum number of steps required to obtain a sorted list.
Input

**Line 1:** an integer `N`.

**Line 2:** a list of `N` numbers that can take the values 0 or 1.

Output

**Line 1 :** The minimum number of steps to regroup all the 1 at the beginning of the list.