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## Learning Opportunities

This puzzle can be solved using the following concepts. Practice using these concepts and improve your skills.

## Goal

Imagine you have a bag, which is filled with N balls. Each ball can have the color black or white. You know that W balls in the bag are white.

If you extract a ball from the bag, the probability changes of the remaining balls.

Your job is it to output the ratio of the odds that you extracted k white balls after extracting s balls from the bag.
Balls are never put back into the bag!

Example:
You have 3 balls in the bag, 2 of which are white.
What is the probability of having 2 white balls by extracting 2 balls?
2/3 * 1/2 = 1/3

When A is the event of getting 2 white balls:
P(A) = Probability of getting 2 white balls = 2/3 * 1/2 = 1/3
P(!A) = Probability of not getting 2 white balls = 1-1/3 = 2/3

So the ratio P(A) : P(!A) is 1:2 (read 1 to 2).

The ratio 2:4 would be the same ratio, but both numbers are divisible by 2, so you need to reduce the ratio.
Input
Line 1: An Integer N for the number of balls in your bag.
Line 2: An Integer W for the number of white balls in your bag.
Line 3: An Integer s for the size of your sample.
Line 4: An Integer k for the desired number of white balls in your sample.
Output
Line 1: A : B, the odds ratio (in lowest terms) that k white balls are in your sample of s balls
Constraints
0 ≤ N ≤ 60
0 ≤ W ≤ N
0 ≤ s ≤ N
0 ≤ k ≤ s
0 ≤ k ≤ W
Example
Input
3
2
2
2
Output
1:2

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