#include<bits/stdc++.h>
using namespace std;
int m, n, xa[1010], xb[1010], ya[1010], yb[1010], dis[1010], vis[1010];
vector<int> cd[1010], w[1010];
queue<int> q;
int dist(int x, int y, int a, int b) {
	return x + y - a + b;
}
signed main() {
	freopen("usaco_Jan_boards.in", "r", stdin);
	freopen("usaco_Jan_boards.out", "w", stdout);
	cin >> m >> n;
	for(int i = 1; i <= n; i ++) {
		cin >> xa[i] >> ya[i] >> xb[i] >> yb[i]; 
	}
	for(int i = 1; i <= n; i ++) {
		for(int j = 1; j <= n; j ++) {
			if(i == j) {
				continue;
			}
			if(xa[j] >= xb[i] && ya[j] >= yb[i]) {
				cd[i].push_back(j);
				w[i].push_back(dist(xa[j], ya[j], xb[i], yb[i]));
			}
		}
	}
	for(int i = 1; i <= n; i ++) {
		cd[0].push_back(i);
		w[0].push_back(dist(xa[i], ya[i], 0, 0));
		if(xb[i] <= m && yb[i] <= m) {
			cd[i].push_back(n + 1);
			w[i].push_back(dist(m, m, xb[i], yb[i]));
		}
	}
	memset(dis, 0x3f, sizeof(dis));
	dis[0] = 0;
	q.push(0);
	while(!q.empty()) {
		int x = q.front();
		q.pop();
		vis[x] = 0;
		for(int i = 0; i < cd[x].size(); i ++) {
			int u = cd[x][i];
			if(dis[x] + w[x][i] < dis[u]) {
				dis[u] = dis[x] + w[x][i];
				if(!vis[u]) {
					vis[u] = 1;
					q.push(u);
				}
			}
		}
	} 
	cout << dis[n];
	return 0;
}