import Data.Graph
import Data.Array.Unboxed

main = interact $ show . def

def = solve . map(map(read :: String -> Int) . words) . lines

solve ([n, _] : ab) = length 
  $ filter(==0) 
  $ elems 
  $ indegree 
  $ buildG(1, n) 
  $ map(\[a, b] -> (a, b)) ab