﻿ ABC207 B - Hydrate - Atcoder

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Score : $200$ points

### Problem Statement

There is a container with $A$ cyan balls. Takahashi will do the following operation as many times as he likes (possibly zero times):

• add $B$ cyan balls and $C$ red balls into the container.

Takahashi's objective is to reach a situation where the number of cyan balls in the container is at most $D$ times the number of red balls in it.

Determine whether the objective is achievable. If it is achievable, find the minimum number of operations needed to achieve it.

### Constraints

• $1 \leq A,B,C,D \leq 10^5$
• All values in input are integers.

### Input

Input is given from Standard Input in the following format:

$A$ $B$ $C$ $D$


### Output

If Takahashi's objective is achievable, print the minimum number of operations needed to achieve it. Otherwise, print -1.

### Sample Input 1

5 2 3 2


### Sample Output 1

2


Before the first operation, the container has $5$ cyan balls and $0$ red balls. Since $5$ is greater than $0$ multiplied by $D=2$, Takahashi's objective is not yet achieved.

Just after the first operation, the container has $7$ cyan balls and $3$ red balls. Since $7$ is greater than $3$ multiplied by $2$, the objective is still not achieved.

Just after the second operation, the container has $9$ cyan balls and $6$ red balls. Since $9$ is not greater than $6$ multiplied by $2$, the objective is achieved.

Thus, the answer is $2$.

### Sample Input 2

6 9 2 3


### Sample Output 2

-1


No matter how many times Takahashi repeats the operation, his objective will never be achieved.