#include<bits/stdc++.h>

#define LL long long

#define fi first

#define se second

#define mk make_pair

#define PLL pair<LL, LL>

#define PLI pair<LL, int>

#define PII pair<int, int>

#define SZ(x) ((int)x.size())

#define ull unsigned long long

using namespace std;

const int N =  + ;

const int inf = 0x3f3f3f3f;

const LL INF = 0x3f3f3f3f3f3f3f3f;

const int mod = 1e9 + ;

const double eps = 1e-;

const double PI = acos(-);

int n, m;

int a[N], f[][N][N];

vector<pair<PII, int>> vc[N];

int main() {

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

    for(int i = ; i <= n; i++) scanf("%d", &a[i]);

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

        int s, f, c, r;

        scanf("%d%d%d%d", &s, &f, &c, &r);

        r = min(f - s + , r + );

        vc[r].push_back(mk(mk(s, f), c));

    }

    LL ans = ;

    int cur = , lst = ;

    for(int i = ; i <= n; i++)

        for(int j = i; j <= n; j++)

            f[cur][i][j] = a[j] - a[i];

    for(int k = ; k <= ; k++) {

        swap(cur, lst);

        for(auto& t : vc[k - ]) {

            ans = max(ans, 1ll * f[lst][t.fi.fi][t.fi.se] * t.se);

        }

        for(int i = ; i <= n; i++) {

            int p = i + k - ;

            for(int j = i + k - ; j <= n; j++) {

                while(p < j && f[lst][i][p] <= a[j] - a[p]) p++;

                f[cur][i][j] = min(f[lst][i][p], a[j] - a[p - ]);

            }

        }

    }

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

    return ;

}

/*

*/