#abc289h. [abc289_h]Trio
[abc289_h]Trio
Problem Statement
On a number line are person , person , and person . At time , person is at point , person is at point , and person is at point .
Here, , , and are all integers, and .
At time , the three people start random walks. Specifically, a person that is at point at time ( is a non-negative integer) moves to point or point at time with equal probability. (All choices of moves are random and independent.)
Find the probability, modulo , that it is at time that the three people are at the same point for the first time.
What is rational number modulo ? We can prove that the sought probability is always a rational number. Moreover, under the Constraints of this problem, when the value is represented as by two coprime integers and , we can prove that there is a unique integer such that and . Find such .
Constraints
- , and are integers.
Input
The input is given from Standard Input in the following format:
Output
Find the probability, modulo , that it is at time that the three people are at the same point for the first time, and print the answer.
Sample Input 1
1 1 3 1
Sample Output 1
873463809
The three people are at the same point for the first time at time with the probability . Since , should be printed.
Sample Input 2
0 0 0 0
Sample Output 2
1
The three people may already be at the same point at time .
Sample Input 3
0 2 8 9
Sample Output 3
744570476
Sample Input 4
47717 21993 74147 76720
Sample Output 4
844927176