#include<bits/stdc++.h>
#define inf INT_MAX
using namespace std;
ifstream fin("felinare.in");
ofstream fout("felinare.out");
int const N = 2e4 + 3;
int st[N] , dr[N] , lv[N];
int n , m , e , a , b;
vector<int> v[N];
queue<int> q;
bool bfs(){
    for(int i = 1 ; i <= n ; ++ i)
        if(!dr[i])
            q.push(i);
        else
            lv[i] = inf;
    lv[0] = inf;
    while(!q.empty()){
        int x = q.front();
        q.pop();
        if(lv[x] < lv[0]){
            for(auto y : v[x]){
                if(lv[st[y]] == inf){
                    lv[st[y]] = 1 + lv[x];
                    q.push(st[y]);
                }
            }
        }
    }
    return lv[0] != inf;

}
bool dfs(int x){
    if(x == 0)
        return true;
    for(auto y : v[x]){
        if(lv[x] + 1 == lv[st[y]] && dfs(st[y])){
            dr[x] = y;
            st[y] = x;
            return true;
        }
    }
    lv[x] = inf;
    return false;
}
int maxmatch(){
    int r = 0;
    fill(st , st + N , 0);
    fill(dr , dr + N , 0);
    while(bfs()){
        for(int i = 1 ; i <= n ; ++ i){
            if(!dr[i] && dfs(i))
                ++ r;
        }
    }
    return r;
}
int main()
{
    fin >> n >> m;
    for(int i = 1 ; i <= m ; ++ i){
        fin >> a >> b;
        v[a].push_back(b + n);
    }
    maxmatch();
    int r = n + n;
    for(int i = 1 ; i <= n ; ++ i)
        if(!dr[i]){
            -- r;
        }
    fout << r
     << '\n';
    return 0;
}