There are $$$n$$$ armchairs, numbered from $$$1$$$ to $$$n$$$ from left to right. Some armchairs are occupied by people (at most one person per armchair), others are not. The number of occupied armchairs is not greater than $$$\frac{n}{2}$$$.

For some reason, you would like to tell people to move from their armchairs to some other ones. If the $$$i$$$-th armchair is occupied by someone and the $$$j$$$-th armchair is not, you can tell the person sitting in the $$$i$$$-th armchair to move to the $$$j$$$-th armchair. The time it takes a person to move from the $$$i$$$-th armchair to the $$$j$$$-th one is $$$|i - j|$$$ minutes. You may perform this operation any number of times, but these operations must be done sequentially, i. e. you cannot tell a person to move until the person you asked to move in the last operation has finished moving to their destination armchair.

You want to achieve the following situation: every seat that was initially occupied must be free. What is the minimum time you need to do it?

Input

The first line contains one integer $$$n$$$ ($$$2 \le n \le 5000$$$) — the number of armchairs.

The second line contains $$$n$$$ integers $$$a_1, a_2, \dots, a_n$$$ ($$$0 \le a_i \le 1$$$). $$$a_i = 1$$$ means that the $$$i$$$-th armchair is initially occupied, $$$a_i = 0$$$ means that it is initially free. The number of occupied armchairs is at most $$$\frac{n}{2}$$$.

Output

Print one integer — the minimum number of minutes you have to spend to achieve the following situation: every seat that was initially occupied must be free.

Note

In the first test, you can perform the following sequence:

ask a person to move from armchair $$$1$$$ to armchair $$$2$$$, it takes $$$1$$$ minute;
ask a person to move from armchair $$$7$$$ to armchair $$$6$$$, it takes $$$1$$$ minute;
ask a person to move from armchair $$$4$$$ to armchair $$$5$$$, it takes $$$1$$$ minute.

In the second test, you can perform the following sequence:

ask a person to move from armchair $$$1$$$ to armchair $$$4$$$, it takes $$$3$$$ minutes;
ask a person to move from armchair $$$2$$$ to armchair $$$6$$$, it takes $$$4$$$ minutes;
ask a person to move from armchair $$$4$$$ to armchair $$$5$$$, it takes $$$1$$$ minute;
ask a person to move from armchair $$$3$$$ to armchair $$$4$$$, it takes $$$1$$$ minute.

In the third test, no seat is occupied so your goal is achieved instantly.

Armchairs

Examples