N,M = map(int,input().split())
import sys
sys.setrecursionlimit(10 ** 6)

parent = [-1] * (M + 1)
def find(i):
    if parent[i] < 0:
        return i
    parent[i] = find(parent[i])
    return parent[i]
def unite(i,j):
    I = find(i)
    J = find(j)
    if I == J:return False
    if -parent[I] > -parent[J]:
        I,J = J,I
    parent[J] += parent[I]
    parent[I] = J
    return True

col = [[] for _ in range(N+1)]
for _ in range(N):
    b,c = map(int,input().split())
    col[c].append(b)
for i in range(1,N+1):
    if len(col[i]) >= 2:
        for b in col[i]:
            unite(b,col[i][0])
ans = 0
for i in range(1,M+1):
    if parent[i] < 0:
        ans += -parent[i] - 1
print(ans)