#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;

typedef long long ll;
typedef modint998244353 mint;
const int MOD = 1000000007;
#define all(x) x.begin(), x.end()
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
const int inf = 1 << 30;
const ll INF = 1LL << 60;
const int dx[8] = {1, 0, -1, 0, -1, -1, 1, 1};
const int dy[8] = {0, 1, 0, -1, -1, 1, -1, 1};
template <class T> bool chmax(T& a, const T& b) { if (a < b) { a = b; return 1; } return 0; }
template <class T> bool chmin(T& a, const T& b) { if (b < a) { a = b; return 1; } return 0; }

int main(){
    int n, m;
    cin >> n >> m;
    //ans = 2 * (n - 1) - 何本近道を使ったか
    map<int, vector<int>> mp;
    rep(i, m){
        int a, b;
        cin >> a >> b;
        mp[a].push_back(b);
    }

    map<int, int> dist;
    for(auto it = mp.begin(); it != mp.end(); it++){
        for(auto b : mp[it->first]){
            chmax(dist[b], dist[it->first] + 1);
        }
    }

    int x = 0;
    for(auto it = dist.begin(); it != dist.end(); it++){
        chmax(x, it->second);
    }

    cout << 2 * (n - 1) - x << endl;

    return 0;
}