use proconio::input;
use ac_library::Dsu;

fn main(){
    input!{
        n: usize,
        m: usize,
        e: [(usize, usize); m],
    }

    let mut uf = Dsu::new(n);
    let mut i = vec![0_i32; n];
    let mut o = vec![0_i32; n];
    for (u, v) in e{
        uf.merge(u-1, v-1);
        i[v-1] += 1;
        o[u-1] += 1;
    }

    let h = uf.groups();
    let mut ans = -1;
    for a in h{
        let mut ok = 0;
        let mut tm = 0;
        for x in a{
            if i[x] > 0{
                ok = 1;
            }
            tm += (o[x]-i[x]).abs();
        }
        ans += (tm/2-1).max(0)+ok;
    }
    println!("{}", ans);
}