human
Bear Limak examines a social network. Its main functionality is that two members can become friends (then they can talk with each other and share funny pictures).

There are n members, numbered 1 through n. m pairs of members are friends. Of course, a member can't be a friend with themselves.

Let A-B denote that members A and B are friends. Limak thinks that a network is reasonable if and only if the following condition is satisfied: For every three distinct members (X, Y, Z), if X-Y and Y-Z then also X-Z.

For example: if Alan and Bob are friends, and Bob and Ciri are friends, then Alan and Ciri should be friends as well.

Can you help Limak and check if the network is reasonable? Print "YES" or "NO" accordingly, without the quotes.

Input

The first line of the input contain two integers n and m (3 ≤ n ≤ 150 000, ) — the number of members and the number of pairs of members that are friends.

The i-th of the next m lines contains two distinct integers ai and bi (1 ≤ ai, bi ≤ n, ai ≠ bi). Members ai and bi are friends with each other. No pair of members will appear more than once in the input.

Output

If the given network is reasonable, print "YES" in a single line (without the quotes). Otherwise, print "NO" in a single line (without the quotes).

Examples

Input

4 3
1 3
3 4
1 4

Output

YES

Input

4 4
3 1
2 3
3 4
1 2

Output

NO

Input

10 4
4 3
5 10
8 9
1 2

Output

YES

Input

3 2
1 2
2 3

Output

NO

Note

The drawings below show the situation in the first sample (on the left) and in the second sample (on the right). Each edge represents two members that are friends. The answer is "NO" in the second sample because members (2, 3) are friends and members (3, 4) are friends, while members (2, 4) are not.

The above is tricky. Write me a correct solution in PYTHON3.

Write me a Python code to print "YES" or "NO" accordingly, without the quotes?
assistant
#Here is Python code to print "YES" or "NO" accordingly, without the quotes.

import sys, os, io
def rs(): return sys.stdin.readline().rstrip()
def ri(): return int(sys.stdin.readline())
def ria(): return list(map(int, sys.stdin.readline().split()))
def ws(s): sys.stdout.write(s + '\n')
def wi(n): sys.stdout.write(str(n) + '\n')
def wia(a): sys.stdout.write(' '.join([str(x) for x in a]) + '\n')
import math,datetime,functools,itertools,operator,bisect,fractions,statistics
from collections import deque,defaultdict,OrderedDict,Counter
from fractions import Fraction
from decimal import Decimal
from sys import stdout
from heapq import heappush, heappop, heapify ,_heapify_max,_heappop_max,nsmallest,nlargest
#sys.setrecursionlimit(111111) 
INF=99999999999999999999999999999999

def main():

    mod=1000000007
    # InverseofNumber(mod)
    # InverseofFactorial(mod)
    # factorial(mod)
    starttime=datetime.datetime.now()
    if(os.path.exists('input.txt')):
        sys.stdin = open("input.txt","r")
        sys.stdout = open("output.txt","w")
    
    ###CODE
    tc = 1
    for _ in range(tc):
        n,m=ria()
        graph=[[] for i in range(n+1)]
        visited=[False]*(n+1)
        col=[-1]*(n+1)
        for i in range(m):
            a,b=ria()
            graph[a].append(b)
            graph[b].append(a)
        
        def dfs(start):
            comp=[]
            stack = [start]
            while stack:
                start = stack[-1]
                # push unvisited children into stack
                if not visited[start]:
                    comp.append(start)
                    visited[start] = True
                    for child in graph[start]:
                        if not visited[child]:
                            stack.append(child)
                else:
                    
                    stack.pop()
            for i in comp:
                if len(graph[i])!=len(comp)-1:
                    return False
            return True
        cc=0
        d={}
        ans="YES"
        for i in range(1,n+1):
            if not visited[i] and not dfs(i):
               ...