mod = 1000000007
eps = 10**-9


def main():
    import sys
    from collections import deque
    input = sys.stdin.readline

    N, M = map(int, input().split())
    seen = [0] * (N+1)
    ans = 0
    box = [set() for _ in range(M+1)]
    for _ in range(N):
        b, c = map(int, input().split())
        box[b].add(c)

    adj = [set() for _ in range(N+1)]
    for b in range(1, M+1):
        C = list(box[b])
        if len(C) > 1:
            c0 = C[0]
            for c in C[1:]:
                adj[c0].add(c)
                adj[c].add(c0)

    root = [-1] * (N+1)
    for v0 in range(1, N+1):
        if seen[v0]:
            continue
        root[v0] = v0
        que = deque()
        que.append(v0)
        seen[1] = 1
        while que:
            v = que.popleft()
            for u in adj[v]:
                if seen[u] == 0:
                    seen[u] = 1
                    que.append(u)
                    root[u] = v0

    cnt = [0] * (N+1)
    for i in range(1, M+1):
        if box[i]:
            b = min(list(box[i]))
            cnt[root[b]] += 1
    for i in range(1, N+1):
        if cnt[i]:
            ans += cnt[i] - 1
    print(ans)


if __name__ == '__main__':
    main()