class UnionFind:
    def __init__(self, n, w=None):
        self.par = [-1]*n
        self.rank = [0]*n
        self.siz = [1]*n
        self.cnt = n
        self.min_node = [i for i in range(n)]
        self.weight = w if w else [1]*n

    def root(self, x):
        if self.par[x] == -1:
            return x
        self.par[x] = self.root(self.par[x])
        return self.par[x]

    def issame(self, x, y):
        return self.root(x) == self.root(y)
            
    def unite(self, x, y):
        px = self.root(x)
        py = self.root(y)
        if px == py:
            return False
        if self.rank[px] < self.rank[py]:
            px, py = py, px
        self.par[py] = px
        if self.rank[px] == self.rank[py]:
            self.rank[px] += 1
        self.siz[px] += self.siz[py]
        self.cnt -= 1
        self.min_node[px] = min(self.min_node[px], self.min_node[py])
        self.weight[px] += self.weight[py]
        return False

    def count(self):
        return self.cnt

    def min(self, x):
        return self.min_node[self.root(x)]

    def getweight(self, x):
        return self.weight[self.root(x)]
    
    def size(self, x):
        return self.siz[self.root(x)]
    
from collections import defaultdict

N, M = map(int, input().split())
UV = [list(map(int, input().split())) for _ in range(M)]
deg = [0 for _ in range(N)]
indeg = [0 for _ in range(N)]
UF = UnionFind(N)
for u, v in UV:
    u-=1
    v-=1
    deg[u] += 1
    indeg[v] += 1
    UF.unite(u, v)
plus = defaultdict(int)
for i in range(N):
    sa = indeg[i]-deg[i]
    r = UF.root(i)
    if sa>0:
        plus[r] += sa

ans = 0
for k in plus:
    if plus[k]>=2:
        ans+=plus[k]-1

ans += len(plus)-1
print(ans)