local n, m = io.read("*n", "*n")
local t = {}
for i = 1, n do t[i] = 1 end
for i = 1, m do
  local a, b = io.read("*n", "*n")
  t[b] = 0
end
local c = 0
for i = 1, n do
  c = c + t[i]
end
print(c)