A loom threads a shuttle across a rectangular field of pins arranged in R rows and C columns. The shuttle starts at the top-left pin and must arrive at the bottom-right pin. On every move it advances to the pin one place to the right, or the pin one place below its current pin. It never moves left, up, or diagonally.
Count how many distinct threading routes reach the bottom-right pin.
Input format
A single line with two integers R and C, separated by a space.
Output format
A single integer: the number of distinct right/down routes from the top-left pin to the bottom-right pin.
Constraints
- 1 <= R <= 30
- 1 <= C <= 30
- The answer is guaranteed to fit in a signed 64-bit integer.