from atcoder.dsu import DSU
N, M = map(int, input().split())
dsu = DSU(M)
E = [[] for _ in range(N)]
for i in range(N):
    b, c = map(int, input().split())
    b -= 1
    c -= 1
    E[c].append(b)
for i in range(N):
    if len(E[i]) > 1:
        e0 = E[i][0]
        for e in E[i][1:]:
            dsu.merge(e0, e)

ans = 0
for i in range(M):
    if dsu.leader(i) == i:
        ans += dsu.size(i) - 1
print(ans)