#include <bits/stdc++.h>

using namespace std;

const int MAXN = 1e5 + 5;

int n, m, cnt, ans;

int u[MAXN], v[MAXN], b[MAXN << 1];

int l[MAXN], r[MAXN];

int fa[MAXN], zhi[MAXN];

vector<int> g[MAXN << 3];

int find(int x) {

    if(fa[x] != x) return find(fa[x]);

    else return x;

}

void update(int ql, int qr, int x, int l, int r, int rt) {

    if(ql <= l && qr >= r) {

        g[rt].push_back(x); //表示l,r区间能通过x号边

        return;

    }

    int mid = l + r >> 1;

    if(ql <= mid) update(ql, qr, x, l, mid, rt << 1);

    if(qr > mid) update(ql, qr, x, mid + 1, r, rt << 1 | 1);

}

void dfs(int l, int r, int rt) {

    vector< pair<int, int> > tmp;

    for(int i = 0; i < g[rt].size(); i++) {

        int x = u[g[rt][i]], y = v[g[rt][i]];

        int fx = find(x), fy = find(y);

        if(fx == fy) continue;

        if(zhi[fx] < zhi[fy]) fa[fx] = fy, tmp.push_back(make_pair(fx, 0));

        else if(zhi[fx] > zhi[fy]) fa[fy] = fx, tmp.push_back(make_pair(fy, 0));

        else zhi[fx]++, fa[fy] = fx, tmp.push_back(make_pair(fy, 1));

    }

    if(find(1) == find(n)) {

        ans += b[r + 1] - b[l];

    } else if(l < r) {

        int mid = l + r >> 1;

        dfs(l, mid, rt << 1);

        dfs(mid + 1, r, rt << 1 | 1);

    }

    for(int i = tmp.size() - 1; i >= 0; i--) {

        zhi[fa[tmp[i].first]] -= tmp[i].second;

        fa[tmp[i].first] = tmp[i].first;

    }

}

int main() {

    ans = 0, cnt = 0;

    scanf("%d%d", &n, &m);

    for(int i = 1; i <= n; i++) fa[i] = i, zhi[i] = 0;

    for(int i = 1; i <= m; i++) {

        scanf("%d%d%d%d", &u[i], &v[i], &l[i], &r[i]);

        b[++cnt] = l[i]; b[++cnt] = r[i] + 1;

    }

    sort(b + 1, b + 1 + cnt);

    cnt = unique(b + 1, b + 1 + cnt) - (b + 1);

    for(int i = 1; i <= m; i++) {

        int t1 = lower_bound(b + 1, b + 1 + cnt, l[i]) - b;

        int t2 = lower_bound(b + 1, b + 1 + cnt, r[i] + 1) - b;

        update(t1, t2 - 1, i, 1, cnt, 1);

    }

    dfs(1, cnt, 1);

    printf("%d\n", ans);

    return 0;

}