过儿！！

#include<bits/stdc++.h>
#define N 200010
using namespace std;
int n, m, a[N], fr[N], to[N], Ans;
struct node {
	int x, y, yy, id;
} p[N];
bool cmp(node aa, node bb) {
	return aa.x == bb.x ? aa.y < bb.y : aa.x < bb.x;
}
bool ycmp(node aa, node bb) {
	return aa.y < bb.y;
}
int ans[N];
void add(int x, int val) {
	for(; x <= m * 2; x += (x & -x)) ans[x] = min(ans[x], val);
} 
int qzh(int x) {
	int Ans = 0; 
	for(; x; x -= (x & -x)) Ans = min(Ans, ans[x]);
	return Ans;
}
int main() {
	scanf("%d%d", &n, &m);
	for(int i = 1; i <= m; i++) {
		scanf("%d%d", &p[i].x, &p[i].y), p[i].id = i;
		scanf("%d%d", &p[i + m].x, &p[i + m].y), p[i + m].id = i;
	}
	sort(p + 1, p + m * 2 + 1, ycmp);
	p[0].y = -1;
	for(int i = 1; i <= 2 * m; i++) p[i].yy = p[i - 1].yy + (p[i - 1].y != p[i].y);
	sort(p + 1, p + m * 2 + 1, cmp);
	for(int i = 1; i <= m * 2; i++) {
		if(fr[p[i].id]) to[p[i].id] = i;
		else fr[p[i].id] = i;
	}
	for(int i = 1; i <= m * 2; i++) {
		a[i] = min(a[i], qzh(p[i].yy));
		if(fr[p[i].id] == i) a[to[p[i].id]] = min(a[to[p[i].id]], 
			a[i] + p[i].x + p[i].y - p[to[p[i].id]].x - p[to[p[i].id]].y);
		add(p[i].yy, a[i]);
		Ans = min(Ans, a[i]);
	}
	printf("%d\n", Ans + n * 2);
	return 0;
}