public class Problem15 {

	//How many such routes are there through a 20×20 grid?
	//137846528820

	public static void main(String[] args) {
		int length = 20;
		long totalPaths[][] = new long[length + 1][length + 1];

		for(int row = 0; row < totalPaths.length; row++){
			for(int column = 0; column < totalPaths[row].length; column++){
				if(row == 0 || column == 0){
					totalPaths[row][column] = 1L;
				}else{
					totalPaths[row][column] = totalPaths[row - 1][column] + totalPaths[row][column - 1];
				}
			}
		}

		System.out.println(totalPaths[length][length]);
	}
}