A triangular number is the number of dots in an equilateral triangle uniformly filled with dots. For example, three dots can be arranged in a triangle; thus three is a triangular number. The n-th triangular number is the number of dots in a triangle with n dots on a side. <image>. You can learn more about these numbers from Wikipedia (http://en.wikipedia.org/wiki/Triangular_number).

Your task is to find out if a given integer is a triangular number.

Input

The first line contains the single number n (1 ≤ n ≤ 500) — the given integer.

Output

If the given integer is a triangular number output YES, otherwise output NO.

Examples

Input

1


Output

YES


Input

2


Output

NO


Input

3


Output

YES
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.Collection;
import java.util.List;
import java.util.Scanner;
import java.util.function.Function;
import java.util.stream.Collectors;
public class _p000047A {
    static public void main(final String[] args) throws IOException {
        p000047A._main(args);
    }
//begin p000047A.java
static private class p000047A extends Solver{public p000047A(){nameIn="p000047A.in"
;singleTest=true;}int n;@Override protected void solve(){int r=(int)Math.ceil(-1
+Math.sqrt(1+8*n))/2;pw.println(r*(r+1)/2==n?"YES":"NO");}@Override public void readInput
()throws IOException{n=sc.nextInt();if(sc.hasNextLine()){sc.nextLine();}}static public
void _main(String[]args)throws IOException{new p000047A().run();}}
//end p000047A.java
//begin net/leksi/contest/Solver.java
static private abstract class Solver{protected String nameIn=null;protected String
nameOut=null;protected boolean singleTest=false;protected boolean preprocessDebug
=false;protected boolean doNotPreprocess=false;protected Scanner sc=null;protected
PrintWriter pw=null;private void process()throws IOException{if(!singleTest){int
t=lineToIntArray()[0];while(t-->0){readInput();solve();}}else{readInput();solve(
);}}abstract protected void readInput()throws IOException;abstract protected void
solve()throws IOException;protected int[]lineToIntArray()throws IOException{return
Arrays.stream(sc.nextLine().trim().split("\\s+")).mapToInt(Integer::valueOf).toArray
();}protected long[]lineToLongArray()throws IOException{return Arrays.stream(sc.nextLine
().trim().split("\\s+")).mapToLong(Long::valueOf).toArray();}protected String joinToString
(final int[]a){return Arrays.stream(a).mapToObj(Integer::toString).collect(Collectors
.joining(" "));}protected String joinToString(final long[]a){return Arrays.stream
(a).mapToObj(Long::toString).collect(Collectors.joining(" "));}protected<T>String
joinToString(final T[]a){return Arrays.stream(a).map(v->v.toString()).collect(Collectors
.joining(" "));}protected<T>String joinToString(final T[]a,final Function<T,String>
toString){return Arrays.stream(a).map(v->v.toString()).collect(Collectors.joining
(" "));}protected<T>String joinToString(final Collection<T>a){return a.stream().map
(v->v.toString()).collect(Collectors.joining(" "));}protected<T>String joinToString
(final Collection<T>a,final Function<T,String>toString){return a.stream().map(v->
toString.apply(v)).collect(Collectors.joining(" "));}protected List<Long>intArrayToLongList
(final int[]a){return Arrays.stream(a).mapToObj(Long::valueOf).collect(Collectors
.toList());}protected List<Integer>toList(final int[]a){return Arrays.stream(a).mapToObj
(Integer::valueOf).collect(Collectors.toList());}protected List<Long>toList(final
long[]a){return Arrays.stream(a).mapToObj(Long::valueOf).collect(Collectors.toList
());}protected void run()throws IOException{boolean done=false;if(nameIn !=null)
{try{try(FileInputStream fis=new FileInputStream(nameIn);PrintWriter pw0=select_output
();){done=true;sc=new Scanner(fis);pw=pw0;process();}}catch(IOException ex){}}if
(!done){try(PrintWriter pw0=select_output();){sc=new Scanner(System.in);pw=pw0;process
();}}}private PrintWriter select_output()throws FileNotFoundException{if(nameOut
!=null){return new PrintWriter(nameOut);}return new PrintWriter(System.out);}}
//end net/leksi/contest/Solver.java
}
