UVA - 10198 - Counting

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.math.BigInteger;


public class Main {

    public static void main(String[] args) throws IOException {
        InputStreamReader isr = new InputStreamReader(System.in);
        BufferedReader br = new BufferedReader(isr);
        StringBuffer sb=new StringBuffer("");
        String m="";
        BigInteger bg[]=new BigInteger[1001];
        bg[1]=BigInteger.valueOf(2);
        bg[2]=BigInteger.valueOf(5);
        bg[3]=BigInteger.valueOf(13);
        for(int i=4;i<1001;i++){
            bg[i]=bg[i-3].add(bg[i-2]).add(bg[i-1].multiply(BigInteger.valueOf(2)));
        }
        int x=0;
            while((m=br.readLine())!=null) {
              x=Integer.parseInt(m);
              sb.append(bg[x]).append("\n");
               }
            System.out.print(sb);
    }
}