func main()
	var n: int :: cui@inputInt()
	var m: int :: cui@inputInt()
	var uni: @UnionFind :: (#@UnionFind).init(m + 1)
	
	var ans: int :: 0
	var boxs: []int :: #[n + 1]int
	for(1, n)
		var b: int :: cui@inputInt()
		var c: int :: cui@inputInt()
		if(boxs[c] = 0)
			do boxs[c] :: b
		else
			var b0: int :: boxs[c]
			if(!uni.same(b, b0))
				do ans :+ 1
				do uni.unite(b, b0)
			end if
		end if
	end for
	do cui@print("\{ans}\n")
end func

class UnionFind()
	var parents: []int
	+func init(n: int): UnionFind
		do me.parents :: [-1].repeat(n)
		ret me
	end func
	+func size(x: int): int
		ret - me.parents[me.root(x)]
	end func
	+func same(x: int, y: int): bool
		ret me.root(x) = me.root(y)
	end func
	+func unite(x: int, y: int): bool
		do x :: me.root(x)
		do y :: me.root(y)
		if(x = y)
			ret false
		end if
		if(me.size(x) < me.size(y))
			do me.parents[y] :+ me.parents[x]
			do me.parents[x] :: y
		else
			do me.parents[x] :+ me.parents[y]
			do me.parents[y] :: x
		end if
		ret true
	end func
	
	func root(x: int): int
		if(me.parents[x] < 0)
			ret x
		else
			do me.parents[x] :: me.root(me.parents[x])
			ret me.parents[x]
		end if
	end func
end class