#include <bits/stdc++.h>
using namespace std;
#define int long long
using ll = long long;
#define f first
#define s second
using node = int;

struct segtree{
    int size;
    vector<node> vals;
    node ne = 0; //a neutral element

    node comb(node a, node b){
        return max(a, b);
    }

    void init(int n){
        size = 1;
        while(size < n){
            size *= 2;
        }
        vals.assign(2 * size, ne);
    }

    void build(vector<node>& a, int x, int lx, int rx){ //build in O(N)
        if(rx - lx == 1){
            if(lx < a.size()){
                vals[x] = a[lx];
            }
            return;
        }
        int m = (lx + rx)/2;
        build(a, 2 * x + 1, lx, m);
        build(a, 2 * x + 2, m, rx);
        vals[x] = comb(vals[2 * x + 1],vals[2 * x + 2]);
    }

    void build(vector<node>&a){
        build(a, 0, 0, size);
    }

    void update(int i, node v, int x, int lx, int rx){
        if(rx - lx == 1){
            vals[x] = v;
            return;
        }
        int m = (lx + rx)/2;
        if(i < m)
            update(i, v, 2 * x + 1, lx, m);
        else
            update(i, v, 2 * x + 2, m, rx);
        vals[x] = comb(vals[2 * x + 1], vals[2 * x + 2]);
    }

    void update(int i, node v){
        update(i, v, 0, 0, size);
    }

    node query(int l, int r, int x, int lx, int rx){//query the range of [l to r-1]
        if(lx >= r || l >= rx)
            return ne;
        if(lx >= l && rx <= r){
            return vals[x];
        }
        int m = (lx + rx)/2;
        node s1 = query(l, r, 2 * x + 1, lx, m);
        node s2 = query(l, r, 2 * x + 2, m, rx);
        return comb(s1, s2);
    }

    node query(int l, int r){
        return query(l, r, 0, 0, size);
    }
}st;

const int mxP = 1e5 + 10;
int n, p, yy[mxP], sp[mxP];
pair<int, int> e[mxP];
array<int, 4> a[mxP];
bool cmp(int e1, int  e2){
    if(a[e1][3] == a[e2][3])
        return a[e1][2] < a[e2][2];
    return a[e1][3] < a[e2][3];
}
bool cmp2(array<int, 4> e1, array<int, 4> e2){
    if(e1[2] == e2[2])
        return e1[3] < e2[3];
    return e1[2] < e2[2];
}
signed main(){
    ios_base::sync_with_stdio(0); cin.tie(0);
    //freopen("boards.in", "r", stdin); freopen("boards.out", "w", stdout);
    cin >> n >> p;
    st.init(p);
    for(int i=0; i < p; i++){
        for(int j=0;j < 4; j++)
            cin >> a[i][j];
        yy[i] = i;
        e[i] = {a[i][3], a[i][2]};
    }
    sort(a, a+p, cmp2);
    sort(yy,yy+p,cmp);
    sort(e, e+p);
    for(int i = 0; i < p; i++){
        sp[yy[i]] = i;
    }
    //for(int i=0; i < p; i++){
        //cerr << e[i].f << " " << e[i].s << "\n";
    //}
    for(int i=0;i<p; i++){
        int bx = a[i][2], by = a[i][3];
        int ax = a[i][0], ay = a[i][1];
        int pos = upper_bound(e, e + p, (pair<int, int>){ay, (ll)1e9}) - e;
        int sv = st.query(0, pos);
        //cerr << i << " " << bx << " " << by << " " << ax << " " << ay << " " << pos << " " << sv << "\n";
        //assert(sp[i]>=pos);
        if(sv >= 2 * n) assert(false); //CODE IS FAILING THIS ASSERT ON TEST CASES
        //assert(bx + by - (ay + ax - sv) >= 0);
        st.update(sp[i], bx + by - (ay + ax - sv));
    }
    //cerr << st.query(0, p) << "\n";
    cout << 2 * n - st.query(0, p) << "\n";
}