Pascal's triangle has the property that every number in the triangle is the sum of the two numbers above it.
1
1 1
1 2 1
1 3 3 1
1 4 6 4 1
1 5 10 10 5 1
You are given two integers R and C. Your task is to find the Cth number on the Rth row.
Input
On the first line read in two space-separated integers
R and
C (1 ≤
C ≤
R ≤ 25).
Output
On the first and only line output the
Cth number on the
Rth row of Pascal's triangle.
Sample Input 1
5 2
Sample Output 1
4