# input
import sys
input = sys.stdin.readline
II = lambda : int(input())
MI = lambda : map(int, input().split())
LI = lambda : list(map(int, input().split()))
SI = lambda : input().rstrip()
LLI = lambda n : [list(map(int, input().split())) for _ in range(n)]
LSI = lambda n : [input().rstrip() for _ in range(n)]
MI_1 = lambda : map(lambda x:int(x)-1, input().split())
LI_1 = lambda : list(map(lambda x:int(x)-1, input().split()))

def graph(n:int, m:int, dir:bool=False, index:int=-1) -> list[set[int]]:
    edge = [set() for i in range(n+1+index)]
    for _ in range(m):
        a,b = map(int, input().split())
        a += index
        b += index
        edge[a].add(b)
        if not dir:
            edge[b].add(a)
    return edge

def graph_w(n:int, m:int, dir:bool=False, index:int=-1) -> list[set[tuple]]:
    edge = [set() for i in range(n+1+index)]
    for _ in range(m):
        a,b,c = map(int, input().split())
        a += index
        b += index
        edge[a].add((b,c))
        if not dir:
            edge[b].add((a,c))
    return edge

mod = 998244353
inf = 1001001001001001001
ordalp = lambda s : ord(s)-65 if s.isupper() else ord(s)-97
ordallalp = lambda s : ord(s)-39 if s.isupper() else ord(s)-97
yes = lambda : print("Yes")
no = lambda : print("No")
yn = lambda flag : print("Yes" if flag else "No")
def acc(a:list[int]):
    sa = [0]*(len(a)+1)
    for i in range(len(a)):
        sa[i+1] = a[i] + sa[i]
    return sa

prinf = lambda ans : print(ans if ans < 1000001001001001001 else -1)
alplow = "abcdefghijklmnopqrstuvwxyz"
alpup = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
alpall = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
URDL = {'U':(-1,0), 'R':(0,1), 'D':(1,0), 'L':(0,-1)}
DIR_4 = [[-1,0],[0,1],[1,0],[0,-1]]
DIR_8 = [[-1,0],[-1,1],[0,1],[1,1],[1,0],[1,-1],[0,-1],[-1,-1]]
DIR_BISHOP = [[-1,1],[1,1],[1,-1],[-1,-1]]
prime60 = [2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53,59]
# import pypyjit
# pypyjit.set_param('max_unroll_recursion=-1')
# sys.setrecursionlimit(10**7)
# sys.set_int_max_str_digits(0)
class MonoidUnionFind:
    """
    mergeの順序はcompでわたせる
    小さいほうにmerge
    """
    def __init__(self, op, e, data, comp = None):
        self.n = len(data)
        self.op = op
        self.e = e
        self.par = [-1]*self.n
        self.data = data
        self.comp = comp
    
    def merge(self, a, b):
        a = self.leader(a)
        b = self.leader(b)
        if a == b: return a
        if self.comp == None:
            if -self.par[a] < -self.par[b]:
                a,b = b,a
        else:
            if self.comp(self.data[a], self.data[b]):
                a,b = b,a
        self.par[a] += self.par[b]
        self.par[b] = a
        self.data[a] = self.op(self.data[a], self.data[b])
        self.data[b] = self.e
        return a
    
    def same(self, a, b):
        return self.leader(a) == self.leader(b)
    
    def leader(self, a):
        if self.par[a] < 0: return a
        self.par[a] = self.leader(self.par[a])
        return self.par[a]
        
    def size(self, a):
        return -self.par[self.leader(a)]
    
    def set(self, a, x):
        self.data[self.leader(a)] = x
    
    def add(self, a, x):
        a = self.leader(a)
        self.data[a] = self.op(self.data[a], x)
    
    def get(self, a):
        return self.data[self.leader(a)]


n,m = MI()
def op(x,y):
    return x+y

uf = MonoidUnionFind(op,0,[0]*(2*10**5 + 100))

c = dict()
order = 0
for i in range(n):
    x,y = MI_1()
    if x in c:
        x = c[x]
    else:
        c[x] = order
        x = order
        order += 1
        
    if y in c:
        y = c[y]
    else:
        c[y] = order
        y = order
        order += 1
        
    uf.add(x,1)
    uf.merge(x,y)
    # print(uf.par)
    
ans = 0
for x in range(order):
    lx = uf.leader(x)
    if lx != x:
        continue
    sx = uf.size(x)
    gx = uf.get(x)
    if sx <= gx:
        ans += sx
    else:
        ans += sx - 1
        
print(ans)