3 3
1 2
2 3
3 1

YES

n, m = map(int, input().split())
parent = list(range(n+1))
def find(x):
    if parent[x] != x:
        parent[x] = find(parent[x])
    return parent[x]
def union(x, y):
    px, py = find(x), find(y)
    if px == py:
        return False
    parent[px] = py
    return True
cycle = False
for _ in range(m):
    u, v = map(int, input().split())
    if not union(u, v):
        cycle = True
print('YES' if cycle else 'NO')