import sys
sys.setrecursionlimit(100000)


def DFS(s):
    used[s] = True
    for i in graph_list[s]:
        if color[s] == color[i] and used[i]:
            return False
        elif not used[i]:
            if color[s] == 1:
                color[i] = 0
            else:
                color[i] = 1
            res = DFS(i)
            if not res:
                return False
    return True


K, M = map(int, input().split())
graph_list = [list() for _ in range(K)]
for i in range(M):
    x, y = map(int, input().split())
    graph_list[x - 1].append(y - 1)
    graph_list[y - 1].append(x - 1)
used = [False] * K
color = [0] * K
answer = DFS(0)
if answer:
    print('YES')
else:
    print('NO')