import sys
input = lambda :sys.stdin.readline()[:-1]
ni = lambda :int(input())
na = lambda :list(map(int,input().split()))
yes = lambda :print("yes");Yes = lambda :print("Yes");YES = lambda : print("YES")
no = lambda :print("no");No = lambda :print("No");NO = lambda : print("NO")
#######################################################################

from collections import defaultdict
 
class UnionFind():
    def __init__(self, n):
        self.n = n
        self.parents = [-1] * n
 
    def find(self, x):
        if self.parents[x] < 0:
            return x
        else:
            self.parents[x] = self.find(self.parents[x])
            return self.parents[x]
 
    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)
 
        if x == y:
            return
 
        if self.parents[x] > self.parents[y]:
            x, y = y, x
 
        self.parents[x] += self.parents[y]
        self.parents[y] = x
 
    def size(self, x):
        return -self.parents[self.find(x)]
 
    def same(self, x, y):
        return self.find(x) == self.find(y)
 
    def members(self, x):
        root = self.find(x)
        return [i for i in range(self.n) if self.find(i) == root]
 
    def roots(self):
        return [i for i, x in enumerate(self.parents) if x < 0]
 
    def group_count(self):
        return len(self.roots())
 
    def all_group_members(self):
        group_members = defaultdict(list)
        for member in range(self.n):
            group_members[self.find(member)].append(member)
        return group_members
 
    def __str__(self):
        return '\n'.join(f'{r}: {m}' for r, m in self.all_group_members().items())
n, m = na()
uf = UnionFind(n)
d = [0 for i in range(n)]
e = [0 for i in range(n)]
for _ in range(m):
    u,v = na()
    u-=1
    v-=1
    d[u] += 1
    d[v] -= 1
    e[u] += 1
    e[v] += 1
    uf.union(u, v)
    
g = uf.all_group_members()
from heapq import *
hq = []
for i in g:
    x = 0
    y = 0
    for j in g[i]:
        x += max(0, d[j])
        y += e[j]
    if y == 0:
        continue
    heappush(hq, -x)
ans = 0
#print(hq)
while len(hq) > 1:
    #print(hq)
    x = -heappop(hq)
    y = -heappop(hq)
    ans += 1
    if x and y:
        heappush(hq, -(x + y-1))
    elif x or y:
        heappush(hq, -x-y)
    else:
        heappush(hq, -1)

print(ans + max(-hq[0]-1, 0))