import sys
input = sys.stdin.readline

class UnionFind(object):
    def __init__(self, n=1):
        self.par = [i for i in range(n)]
        self.rank = [0 for _ in range(n)]
        self.size = [1 for _ in range(n)]

    def find(self, x):
        if self.par[x] == x:
            return x
        else:
            self.par[x] = self.find(self.par[x])
            return self.par[x]

    def union(self, x, y):
        x = self.find(x)
        y = self.find(y)
        if x != y:
            if self.rank[x] < self.rank[y]:
                x, y = y, x
            if self.rank[x] == self.rank[y]:
                self.rank[x] += 1
            self.par[y] = x
            self.size[x] += self.size[y]

    def is_same(self, x, y):
        return self.find(x) == self.find(y)

    def get_size(self, x):
        x = self.find(x)
        return self.size[x]



N, M = map(int, input().split())
S, T = [0] * N, [0] * N
U = UnionFind(N)
for i in range(M):
    u, v = map(int, input().split())
    u, v = u - 1, v - 1
    U.union(u, v)
    S[u] += 1
    T[v] += 1
    
ans = 0
SS = set()
for i in range(N):
    ans += max(0, S[i] - T[i])
    if S[i] == T[i] == 0:
        continue
    SS.add(U.find(i))
if ans == 0:
    print(len(SS) - 1)
else:
    print(max(0, ans - 1 + len(SS) - 1))