class UnionFind:
    def __init__(self, n):
        self.parent = [-1] * n
        self.size = [1] * n
    def find(self, x):
        if self.parent[x] == -1: return x
        self.parent[x] = self.find(self.parent[x])
        return self.parent[x]
    def union(self, x, y):
        px = self.find(x)
        py = self.find(y)
        if px == py: return
        if self.size[px] < self.size[py]: px, py = py, px
        self.parent[py] = px
        self.size[px] += self.size[py]
    def same(self, x, y):
        return self.find(x) == self.find(y)
    def get_size(self, x):
        return self.size[self.find(x)]
    def get_all_groups(self):
        n = len(self.parent)
        groups = [[] for _ in range(n)]
        for i in range(n):
            groups[self.find(i)].append(i)
        return list(filter(lambda x: x, groups))

N, M = map(int, input().split())
G = [[] for _ in range(N+1)]
for _ in range(N):
    b, c = map(int, input().split())
    G[c].append(b)

uf = UnionFind(M+1)
ans = 0
for col in G:
    for box in col:
        if not uf.same(col[0], box):
            uf.union(col[0], box)
            ans += 1
print(ans)