CF965C.Greedy Arkady

$k$ people want to split $n$ candies between them. Each candy should be given to exactly one of them or be thrown away.

The people are numbered from $1$ to $k$ , and Arkady is the first of them. To split the candies, Arkady will choose an integer $x$ and then give the first $x$ candies to himself, the next $x$ candies to the second person, the next $x$ candies to the third person and so on in a cycle. The leftover (the remainder that is not divisible by $x$ ) will be thrown away.

Arkady can't choose $x$ greater than $M$ as it is considered greedy. Also, he can't choose such a small $x$ that some person will receive candies more than $D$ times, as it is considered a slow splitting.

Please find what is the maximum number of candies Arkady can receive by choosing some valid $x$ .

The only line contains four integers $n$ , $k$ , $M$ and $D$ ( $2 \le n \le 10^{18}$ , $2 \le k \le n$ , $1 \le M \le n$ , $1 \le D \le \min{(n, 1000)}$ , $M \cdot D \cdot k \ge n$ ) — the number of candies, the number of people, the maximum number of candies given to a person at once, the maximum number of times a person can receive candies.

Print a single integer — the maximum possible number of candies Arkady can give to himself.

Note that it is always possible to choose some valid $x$ .

In the first example Arkady should choose $x = 4$ . He will give $4$ candies to himself, $4$ candies to the second person, $4$ candies to the third person, then $4$ candies to the fourth person and then again $4$ candies to himself. No person is given candies more than $2$ times, and Arkady receives $8$ candies in total.

Note that if Arkady chooses $x = 5$ , he will receive only $5$ candies, and if he chooses $x = 3$ , he will receive only $3 + 3 = 6$ candies as well as the second person, the third and the fourth persons will receive $3$ candies, and $2$ candies will be thrown away. He can't choose $x = 1$ nor $x = 2$ because in these cases he will receive candies more than $2$ times.

In the second example Arkady has to choose $x = 4$ , because any smaller value leads to him receiving candies more than $1$ time.