local n, m = io.read("*n", "*n")
local col = {}

for i = 1, n do
  col[i] = {}
end
for i = 1, n do
  local b, c = io.read("*n", "*n")
  table.insert(col[c], b)
end

local parent = {}
for i = 1, m do
  parent[i] = i
end

local function uf_findroot(idx)
  local idx_update = idx
  while parent[idx] ~= idx do
    idx = parent[idx]
  end
  while parent[idx_update] ~= idx do
    parent[idx_update], idx_update = idx, parent[idx_update]
  end
  return idx
end
local ret = 0
for icol = 1, n do
  if 1 < #col[icol] then
    local r = uf_findroot(col[icol][1])
    for i = 2, #col[icol] do
      local b = col[icol][i]
      local rb = uf_findroot(b)
      if rb ~= r then
        ret = ret + 1
        parent[rb], parent[b] = r, r
      end
    end
  end
end
print(ret)