class UnionFind():
    def __init__(self,n):
        self.par = [-1] * n
        self.rank = [0] * n
        self.siz = [1] * n
    
    def root(self,x):
        if self.par[x] == -1:
            return x
        else:
            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):
        rx = self.root(x)
        ry = self.root(y)
        if rx == ry:
            return False
        if self.rank[rx] < self.rank[ry]:
            rx,ry = ry,rx
        self.par[ry] = rx
        if self.rank[rx] == self.rank[ry]:
            self.rank[rx] += 1
        self.siz[rx] += self.siz[ry]
        return True
    
    def size(self,x):
        return self.siz[self.root(x)]

N,M = map(int,input().split())
uf = UnionFind(N+1)
L = [[] for i in range(N+1)]
for i in range(N):
    b,c = map(int, input().split())
    L[c].append(b)

uf = UnionFind(M+1)
cnt = 0
for l in L:
    for c in l:
        if not uf.issame(l[0],c):
            uf.unite(l[0],c)
            cnt+=1
print(cnt)