N,M = map(int,input().split())

"""
parent = list(range(N+1))
import sys

sys.setrecursionlimit(10 ** 8)
def find(i):
    if parent[i] == i:return i
    parent[i] = find(parent[i])
    return parent[i]
def unite(i,j):
    I = find(i)
    J = find(j)
    if I == J:return False
    parent[I] = J
    parent[i] = J
    return True
for _ in range(M):
    a,b = map(int,input().split())
    unite(a,b)
ans = 0
"""
G = [0] * (N+1)
rG = [0] * (N + 1)
for _ in range(M):
    a,b = map(int,input().split())
    G[a] += 1
    rG[b] += 1
count1
count2
for i in range(1,N+1):
    if G[i] == 0:
        count1 += 1
    if rG[i] == 0:
        count2 += 1
print(max(count1,count2))