import sys
input = sys.stdin.readline

def main():
    N, M = map(int, input().split())
    
    l = [list(map(int, input().split())) for l in range(M)]

    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 roots(self):
            return [i for i, x in enumerate(self.parents) if x < 0]
        def group_count(self):
            return len(self.roots())

    lout = [0] * N
    lin = [0] * N
    lans = [0] * N

    uf = UnionFind(N)
    
    for i in range(M):
        uf.union(l[i][0] - 1, l[i][1] - 1)
        lout[l[i][0] - 1] += 1
        lin[l[i][1] - 1] += 1
    
    ecpt = 0
    
    for i in range(N):
        lans[i] = lout[i] - lin[i]
        if lout[i] == lin[i] == 0:
            ecpt += 1
        
    rc = uf.group_count()

    if set(lans) == {0}:
        print(rc - 1 - ecpt)
    else:
        print(sum([i for i in lans if i > 0]) - 1 + (rc - 1) - ecpt)

if __name__ == '__main__':
    main()