#include <bits/stdc++.h>
using namespace std;
const int NMAX = 400;
const int QMAX = 25e4;
const int LEN = 1e4;
const long long inf = 1LL << 60;
char buff[LEN];
int ind = LEN - 1;
int i32() {
  int ans = 0;
  while (buff[ind] < '0' || buff[ind] > '9') {
    if (++ind >= LEN) {
      ind = 0;
      fread(buff, 1, LEN, stdin);
    }
  }
  while (!(buff[ind] < '0' || buff[ind] > '9')) {
    ans = ans * 10 + (buff[ind] - '0');
    if (++ind >= LEN) {
      ind = 0;
      fread(buff, 1, LEN, stdin);
    }
  }
  return ans;
}
int n, q;
int a[NMAX + 5];
long long dp[2][NMAX + 5][NMAX + 5];
long long pref_sum[NMAX + 5];
vector<pair<pair<int, int>, int> > v[NMAX + 5];
int main() {
  n = i32();
  q = i32();
  for (int i = 1; i <= n; i++) {
    a[i] = i32();
    pref_sum[i] = a[i];
  }
  for (int j = 1; j <= n; j++) {
    for (int k = 1; k <= j; k++) {
      dp[1][j][k] = inf;
    }
    for (int k = j + 1; k <= n; k++) {
      dp[1][j][k] = a[k] - a[j];
    }
  }
  long long ans = 0;
  while (q--) {
    int s, f, c, r;
    s = i32();
    f = i32();
    c = i32();
    r = i32();
    v[min(f - s, r + 1)].push_back({{s, f}, c});
  }
  for (int i = 2, l = 0; i <= n; i++, l ^= 1) {
    for (int j = 1; j <= n; j++) {
      int pref = j;
      for (int k = 1; k <= j; k++) {
        dp[l][j][k] = inf;
      }
      for (int k = j + 1; k <= n; k++) {
        while (pref + 1 < k &&
               dp[l ^ 1][j][pref + 1] <= pref_sum[k] - pref_sum[pref + 1]) {
          pref++;
        }
        dp[l][j][k] = min(pref_sum[k] - pref_sum[pref], dp[l ^ 1][j][pref + 1]);
        dp[l][j][k] = min(dp[l][j][k], dp[l ^ 1][j][k]);
      }
    }
    for (auto it : v[i]) {
      ans = max(ans, 1LL * dp[l][it.first.first][it.first.second] * it.second);
    }
  }
  for (auto it : v[1]) {
    ans = max(ans, 1LL * (a[it.first.second] - a[it.first.first]) * it.second);
  }
  printf("%lld\n", ans);
  return 0;
}
