[2색칠하기]

import sys
MAX = 100010
N,M = map(int, sys.stdin.readline().split())
graph=[[] for _ in range(MAX)]
check = [False] *(MAX)
board = [[0] for _ in range(MAX)]
flag= False

def dfs(node, color):
  global flag
  check[node] = True
  board[node] = color
  if color ==1:
    other = 2
  else:
    other = 1
  for adj in graph[node]:
    next_node = adj
    if board[next_node] ==color:
      flag = True
      return flag
    if check[next_node]==False:
      dfs(next_node, other)
  return flag

for i in range(M):
  a, b = map(int, sys.stdin.readline().split())
  graph[a].append(b)
  graph[b].append(a)
  
dfs(0,1)
if flag == False:
  print('YES')
else:
  print('NO')