#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return true; } return false; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return true; } return false; }
#define all(x) (x).begin(),(x).end()
#define fi first
#define se second
#define mp make_pair
#define si(x) int(x.size())
const int mod=998244353,MAX=300005;
const ll INF=15LL<<58;


/**
 * Author: Simon Lindholm
 * Date: 2017-04-20
 * License: CC0
 * Source: own work
 * Description: Container where you can add lines of the form kx+m, and query maximum values at points x.
 *  Useful for dynamic programming (``convex hull trick'').
 * Time: O(\log N)
 * Status: stress-tested
 */
#pragma once

struct Line {
    mutable ll k, m, p;
    bool operator<(const Line& o) const { return k < o.k; }
    bool operator<(ll x) const { return p < x; }
};

struct LineContainerMIN : multiset<Line, less<>> {
    // (for doubles, use inf = 1/.0, div(a,b) = a/b)
    static const ll inf = LLONG_MAX;
    ll div(ll a, ll b) { // floored division
        return a / b - ((a ^ b) < 0 && a % b); }
    bool isect(iterator x, iterator y) {
        if (y == end()) return x->p = inf, 0;
        if (x->k == y->k) x->p = x->m > y->m ? inf : -inf;
        else x->p = div(y->m - x->m, x->k - y->k);
        return x->p >= y->p;
    }
    void add(ll k, ll m) {
        k*=-1;m*=-1;
        auto z = insert({k, m, 0}), y = z++, x = y;
        while (isect(y, z)) z = erase(z);
        if (x != begin() && isect(--x, y)) isect(x, y = erase(y));
        while ((y = x) != begin() && (--x)->p >= y->p)
            isect(x, erase(y));
    }
    ll query(ll x) {
        assert(!empty());
        auto l = *lower_bound(x);
        return -(l.k * x + l.m);
    }
};

ll dis1[MAX],dis2[MAX];

vector<pair<int,ll>> G[MAX];

int main(){
    
    std::ifstream in("text.txt");
    std::cin.rdbuf(in.rdbuf());
    cin.tie(0);
    ios::sync_with_stdio(false);
    
    ll N,M;cin>>N>>M;
    vector<ll> W(N);
    for(int i=0;i<N;i++) cin>>W[i];
    
    for(int i=0;i<M;i++){
        ll a,b,c;cin>>a>>b>>c;a--;b--;
        G[a].push_back(mp(b,c));
        G[b].push_back(mp(a,c));
    }
    
    for(int i=0;i<N;i++){
        dis1[i]=INF;
        dis2[i]=INF;
    }
    
    {
        dis1[0]=0;
        priority_queue<pair<ll,ll>,vector<pair<ll,ll>>,greater<pair<ll,ll>>> PQ;
        PQ.push(mp(0,0));
        
        while(!PQ.empty()){
            auto [d,u]=PQ.top();PQ.pop();
            if(dis1[u]<d) continue;
            for(auto [to,co]:G[u]){
                if(chmin(dis1[to],dis1[u]+co)) PQ.push(mp(dis1[to],to));
            }
        }
    }
    
    {
        dis2[N-1]=0;
        priority_queue<pair<ll,ll>,vector<pair<ll,ll>>,greater<pair<ll,ll>>> PQ;
        PQ.push(mp(0,N-1));
        
        while(!PQ.empty()){
            auto [d,u]=PQ.top();PQ.pop();
            if(dis2[u]<d) continue;
            for(auto [to,co]:G[u]){
                if(chmin(dis2[to],dis2[u]+co)) PQ.push(mp(dis2[to],to));
            }
        }
    }
    
    ll ans=dis1[N-1];
    
    LineContainerMIN cht;
    for(int i=0;i<N;i++){
        cht.add(W[i],dis2[i]);
    }
    for(int i=0;i<N;i++){
        chmin(ans,cht.query(W[i])+dis1[i]);
    }
    
    cout<<ans<<endl;
}