fn main() {
    let (n, m): (usize, usize) = {
        let mut line: String = String::new();
        std::io::stdin().read_line(&mut line).unwrap();
        let mut iter = line.split_whitespace();
        (
            iter.next().unwrap().parse().unwrap(),
            iter.next().unwrap().parse().unwrap(),

        )
    };

    let mut indeg:Vec<usize>=vec![0;n+1];

    for _ in 0..m{
        let (a, b): (usize, usize) = {
            let mut line: String = String::new();
            std::io::stdin().read_line(&mut line).unwrap();
            let mut iter = line.split_whitespace();
            (
                iter.next().unwrap().parse().unwrap(),
                iter.next().unwrap().parse().unwrap(),
    
            )
        };

        indeg[b]+=1;
    }

    let mut ans=0;

    for i in 1..n+1{
        if indeg[i]==0{
            ans+=1;
        }
    }

    println!("{}",ans);

}