pascal

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 C^th number on the R^th 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 C^th number on the R^th row of Pascal's triangle.

Sample Input 1

5 2

Sample Output 1

4