import sys
input = sys.stdin.readline

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

E=[list(map(int,input().split())) for i in range(M)]

IN=[0]*(N+1)
OUT=[0]*(N+1)

# UnionFind

Group = [i for i in range(N+1)] # グループ分け
Nodes = [1]*(N+1) # 各グループのノードの数

def find(x):
    while Group[x] != x:
        x=Group[x]
    return x

def Union(x,y):
    if find(x) != find(y):
        if Nodes[find(x)] < Nodes[find(y)]:
            
            Nodes[find(y)] += Nodes[find(x)]
            Nodes[find(x)] = 0
            Group[find(x)] = find(y)
            
        else:
            Nodes[find(x)] += Nodes[find(y)]
            Nodes[find(y)] = 0
            Group[find(y)] = find(x)

for a,b in E:
    Union(a,b)

LEN=0
for i in range(1,N+1):
    if find(i)==i:
        LEN+=1

for a,b in E:
    IN[a]+=1
    OUT[b]+=1

INP=0

for i in range(1,N+1):
    if IN[i]>OUT[i]:
        INP+=IN[i]-OUT[i]


print(max(INP-1,LEN-1))