It is a balmy spring afternoon, and Farmer John's n cows are ruminating about link-cut cacti in their stalls. The cows, labeled 1 through n, are arranged so that the i-th cow occupies the i-th stall from the left. However, Elsie, after realizing that she will forever live in the shadows beyond Bessie's limelight, has formed the Mischievous Mess Makers and is plotting to disrupt this beautiful pastoral rhythm. While Farmer John takes his k minute long nap, Elsie and the Mess Makers plan to repeatedly choose two distinct stalls and swap the cows occupying those stalls, making no more than one swap each minute.

Being the meticulous pranksters that they are, the Mischievous Mess Makers would like to know the maximum messiness attainable in the k minutes that they have. We denote as pi the label of the cow in the i-th stall. The messiness of an arrangement of cows is defined as the number of pairs (i, j) such that i < j and pi > pj.

Input

The first line of the input contains two integers n and k (1 ≤ n, k ≤ 100 000) — the number of cows and the length of Farmer John's nap, respectively.

Output

Output a single integer, the maximum messiness that the Mischievous Mess Makers can achieve by performing no more than k swaps. 

Examples

Input

5 2


Output

10


Input

1 10


Output

0

Note

In the first sample, the Mischievous Mess Makers can swap the cows in the stalls 1 and 5 during the first minute, then the cows in stalls 2 and 4 during the second minute. This reverses the arrangement of cows, giving us a total messiness of 10.

In the second sample, there is only one cow, so the maximum possible messiness is 0.
import java.io.File;import java.io.FileInputStream;import java.io.FileNotFoundException;
import java.io.IOException;import java.io.InputStream;import java.io.PrintWriter;
import java.security.AccessControlException;import java.util.List;public class _p000654B {
static public void main(final String[] args) throws IOException{p000654B._main(args);}

static class p000654B extends Solver{public p000654B(){singleTest=true;}@Override public 
void solve()throws IOException{int n=sc.nextInt();int k=sc.nextInt();sc.nextLine();
long res=0;for(int i=1;i<=k;i++){if(i>=n+1-i){break;}int cur=(n-i*2+1)*2-1;if(cur
<=0){break;}res+=cur;}pw.println(res);}static public void _main(String[]args)throws 
IOException{new p000654B().run();}}static class MyScanner{private StringBuilder 
cache=new StringBuilder();int cache_pos=0;private int first_linebreak=-1;private 
int second_linebreak=-1;private StringBuilder sb=new StringBuilder();private InputStream 
is=null;public MyScanner(final InputStream is){this.is=is;}public String charToString(final 
int c){return String.format("'%s'",c=='\n'?"\\n":(c=='\r'?"\\r":String.valueOf((char)c)));
}public int get(){int res=-1;if(cache_pos<cache.length()){res=cache.charAt(cache_pos);
cache_pos++;if(cache_pos==cache.length()){cache.delete(0,cache_pos);cache_pos=0;
}}else{try{res=is.read();}catch(IOException ex){throw new RuntimeException(ex);}
}return res;}private void unget(final int c){if(cache_pos==0){cache.insert(0,(char)c);
}else{cache_pos--;}}public String nextLine(){sb.delete(0,sb.length());int c;boolean 
done=false;boolean end=false;while((c=get())!=-1){if(check_linebreak(c)){done=true;
if(c==first_linebreak){if(!end){end=true;}else{cache.append((char)c);break;}}else 
if(second_linebreak!=-1 && c==second_linebreak){break;}}if(end && c!=first_linebreak 
&& c!=second_linebreak){cache.append((char)c);break;}if(!done){sb.append((char)c);
}}return!done && sb.length()==0?null:sb.toString();}private boolean check_linebreak(int 
c){if(c=='\n'|| c=='\r'){if(first_linebreak==-1){first_linebreak=c;}else if(c!=first_linebreak 
&& second_linebreak==-1){second_linebreak=c;}return true;}return false;}public int 
nextInt(){return Integer.parseInt(next());}public long nextLong(){return Long.parseLong(next());
}public boolean hasNext(){boolean res=false;int c;while((c=get())!=-1){if(!check_linebreak(c)
&& c!=' '&& c!='\t'){res=true;unget(c);break;}}return res;}public String next(){
sb.delete(0,sb.length());boolean started=false;int c;while((c=get())!=-1){if(check_linebreak(c)
|| c==' '|| c=='\t'){if(started){unget(c);break;}}else{started=true;sb.append((char)c);
}}return sb.toString();}public int nextChar(){return get();}public boolean eof()
{int c=get();boolean res=false;if(c!=-1){unget(c);}else{res=true;}return res;}public 
double nextDouble(){return Double.parseDouble(next());}}static abstract class Solver
{protected String nameIn=null;protected String nameOut=null;protected boolean singleTest
=false;protected MyScanner sc=null;protected PrintWriter pw=null;private int current_test
=0;private int count_tests=0;protected int currentTest(){return current_test;}protected 
int countTests(){return count_tests;}private void process()throws IOException{if(!singleTest)
{count_tests=sc.nextInt();sc.nextLine();for(current_test=1;current_test<=count_tests;
current_test++){solve();pw.flush();}}else{count_tests=1;current_test=1;solve();}
}abstract protected void solve()throws IOException;public void run()throws IOException
{boolean done=false;try{if(nameIn!=null){if(new File(nameIn).exists()){try(FileInputStream 
fis=new FileInputStream(nameIn);PrintWriter pw0=select_output();){select_output();
done=true;sc=new MyScanner(fis);pw=pw0;process();}}else{throw new RuntimeException("File "
+new File(nameIn).getAbsolutePath()+" does not exist!");}}}catch(IOException | AccessControlException 
ex){}if(!done){try(PrintWriter pw0=select_output();){sc=new MyScanner(System.in);
pw=pw0;process();}}}private PrintWriter select_output()throws FileNotFoundException
{if(nameOut!=null){return new PrintWriter(nameOut);}return new PrintWriter(System.out);
}}static abstract class Tester{static public int getRandomInt(final int min,final 
int max){return(min+(int)Math.floor(Math.random()*(max-min+1)));}static public long 
getRandomLong(final long min,final long max){return(min+(long)Math.floor(Math.random()
*(max-min+1)));}static public double getRandomDouble(final double min,final double 
maxExclusive){return(min+Math.random()*(maxExclusive-min));}abstract protected void 
testOutput(final List<String>output_data);abstract protected void generateInput();
abstract protected String inputDataToString();private boolean break_tester=false;
protected void beforeTesting(){}protected void breakTester(){break_tester=true;}
public boolean broken(){return break_tester;}}}
