Poj Solution 2757

http://poj.org/problem?id=2757

//* @author: ccQ.SuperSupper
import java.io.*;
import java.util.*;
import java.math.*;
public class Main 
{
 public static void main(String args[]) throws Exception {
    
    Scanner cin=new Scanner(System.in);
    BigInteger n;
    long b;
    while(cin.hasNext())
    {
        n=cin.nextBigInteger();
        b=cin.nextLong();
        if(n.compareTo(BigInteger.ZERO)<=0)
        {
            System.out.println("0");
            continue;
        }
        BigInteger ans;
        ans=n.multiply(n.add(BigInteger.ONE)).divide(BigInteger.valueOf(2));
        ans=ans.multiply(BigInteger.valueOf(b));
        //how many [0..b-1]
        BigInteger cnt=n.divide(BigInteger.valueOf(b));
        ans=ans.add(BigInteger.valueOf(b*(b-1)/2).multiply(cnt));
        cnt=cnt.multiply(BigInteger.valueOf(b));
        while(cnt.compareTo(n)<=0)
        {
            BigInteger tmp=BigInteger.ZERO,tsum=cnt;
            while(tsum.compareTo(BigInteger.ZERO)>0)
            {
                tmp=tmp.add(tsum.mod(BigInteger.valueOf(b)));
                tsum=tsum.divide(BigInteger.valueOf(b));
            }
             tmp=(BigInteger.valueOf(b).subtract(tmp.mod(BigInteger.valueOf(b)))).mod(BigInteger.valueOf(b));
            cnt=cnt.add(BigInteger.ONE);
            ans=ans.add(tmp);
        }
        System.out.println(ans);
    }
  }
}