Problem Description

There are $n$ balls, of which $k$ are orange and the rest are green. Determine the minimum number of green balls that need to be added to ensure that the proportion of orange balls is less than or equal to $\dfrac{p}{q}$.

If there are $a$ balls in total and $b$ of them are orange, the proportion of orange balls is $\dfrac{b}{a}$.

Input Format

A single line containing four integers $n, k, p, q$.

Output Format

A single line containing one integer, representing the answer.

Sample Input and Output

Sample Input #1

3 3 5 6

Sample Output #1

1

Sample Input #2

3 2 5 6

Sample Output #2

0

Notes/Hints

Data Range and Constraints

For $30\%$ of the test cases, $q = 1$.
For another $30\%$ of the test cases, $k = 0$.
For $100\%$ of the test cases, $1 \leq n, q \leq 1000$, $0 \leq k \leq 1000$, $0 \leq p \leq q$.

见题面 Input 部分

见题面 Output 部分