UVa 10523 - Very Easy !!!

//\\__ hr1212 __//\\

import java.io.*;
import java.math.*;
import java.util.*;

public class Main{

static int n,m,z,x,y,j,k,l,r;
static int a[];
static char x1[],y1[];
static String s,p,q[];
static int MAX=1000010;

public static void main(String[] args) throws IOException{
InputReader in=new InputReader(System.in);
BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
PrintWriter out=new PrintWriter(System.out);
while((s=br.readLine())!=null){
BigInteger b1=BigInteger.ZERO;
BigInteger b2=BigInteger.ZERO,b3=BigInteger.ZERO,i=BigInteger.ONE,ans=BigInteger.ZERO;
q=new String[5];
q=s.split("\\s+");
b1=new BigInteger(q[0]);
b2=new BigInteger(q[1]);
x=1;
while(i.compareTo(b1)!=1){
ans=ans.add(i.multiply(b2.pow(x)));
x++;
i=i.add(BigInteger.ONE);
}
System.out.println(ans);
}


out.close();

}
static class InputReader {

private InputStream stream;
private byte[] buf = new byte[8192];
private int curChar;
private int snumChars;
private SpaceCharFilter filter;

public InputReader(InputStream stream) {
this.stream = stream;
}

public int snext() {
if (snumChars == -1)
throw new InputMismatchException();
if (curChar >= snumChars) {
curChar = 0;
try {
snumChars = stream.read(buf);
} catch (IOException e) {
throw new InputMismatchException();
}
if (snumChars <= 0)
return -1;
}
return buf[curChar++];
}

public int nextInt() {
int c = snext();
while (isSpaceChar(c))
c = snext();
int sgn = 1;
if (c == '-') {
sgn = -1;
c = snext();
}

int res = 0;

do {
if (c < '0' || c > '9')
throw new InputMismatchException();
res *= 10;
res += c - '0';
c = snext();
} while (!isSpaceChar(c));

return res * sgn;
}

public long nextLong() {
int c = snext();
while (isSpaceChar(c))
c = snext();
int sgn = 1;
if (c == '-') {
sgn = -1;
c = snext();
}

long res = 0;

do {
if (c < '0' || c > '9')
throw new InputMismatchException();
res *= 10;
res += c - '0';
c = snext();
} while (!isSpaceChar(c));

return res * sgn;
}

public String readString() {
int c = snext();
while (isSpaceChar(c))
c = snext();
StringBuilder res = new StringBuilder();
do {
res.appendCodePoint(c);
c = snext();
} while (!isSpaceChar(c));
return res.toString();
}

public boolean isSpaceChar(int c) {
if (filter != null)
return filter.isSpaceChar(c);
return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
}

public interface SpaceCharFilter {
public boolean isSpaceChar(int ch);
}
}
}