poj 2084

递推公式 k(n)=(4n-2)/(n+1)*k(n-1)
通项公式 k(n)=c(2n,n)/(n+1) = 2n!/n!/(n-1)
h(0) = 1;

import java.math.BigInteger;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = 0;
        while(sc.hasNext()){
            n = sc.nextInt();
            if(n == -1)
                break;
            BigInteger a = new BigInteger("1"), b = new BigInteger("1"), c = new BigInteger("1");
            for(int i = 1;i <= 2 * n;i++){
                a = a.multiply(b);
                b = b.add(BigInteger.ONE);
                if(i == n)
                    c = a;
            }
            System.out.println(a.divide(c).divide(c).divide(new BigInteger(Integer.toString(n+1))));
        }
    }
}