import std.conv, std.functional, std.range, std.stdio, std.string;
import std.algorithm, std.array, std.bigint, std.bitmanip, std.complex, std.container, std.math, std.mathspecial, std.numeric, std.regex, std.typecons;
import core.bitop;

class EOFException : Throwable { this() { super("EOF"); } }
string[] tokens;
string readToken() { for (; tokens.empty; ) { if (stdin.eof) { throw new EOFException; } tokens = readln.split; } auto token = tokens.front; tokens.popFront; return token; }
int readInt() { return readToken.to!int; }
long readLong() { return readToken.to!long; }

string COLOR(string s = "") { return "\x1b[" ~ s ~ "m"; }

bool chmin(T)(ref T t, in T f) { if (t > f) { t = f; return true; } else { return false; } }
bool chmax(T)(ref T t, in T f) { if (t < f) { t = f; return true; } else { return false; } }

int binarySearch(alias pred, T)(in T[] as) { int lo = -1, hi = cast(int)(as.length); for (; lo + 1 < hi; ) { const mid = (lo + hi) >> 1; (unaryFun!pred(as[mid]) ? hi : lo) = mid; } return hi; }
int lowerBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a >= val)); }
int upperBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a > val)); }


// class Func = TX -> TY
//   For any f, g: Func, x -> sgn(g(x) - f(x)) must be monotone on [L, R].
class LiChaoTree(Func) {
  import std.algorithm : swap;
  alias TX = Func.TX;
  alias TY = Func.TY;
  const(TX) L, R;
  class Tree {
    Tree l, r;
    Func f;
    this(Func f) {
      this.f = f;
    }
  }
  Tree root;

  // [L, R)
  this(TX L, TX R) {
    assert(L < R, "LiChaoTree: L < R must hold");
    this.L = L;
    this.R = R;
  }
  // Add g to the whole [L, R)
  void add(Func g) {
    root = add(root, L, R, g);
  }
  // Add g to [a, b)
  void add(TX a, TX b, Func g) {
    root = add(root, L, R, a, b, g);
  }
  // Get max at a
  TY opCall(TX a) {
    TY mx = TY.min;
    TX l = L, r = R;
    for (Tree u = root; u; ) {
      if (u.f) {
        const fX = u.f(a);
        if (mx < fX) mx = fX;
      }
      const mid = l + (r - l) / 2;
      if (a < mid) {
        u = u.l; r = mid;
      } else {
        u = u.r; l = mid;
      }
    }
    return mx;
  }

 private:
  Tree add(Tree u0, TX l, TX r, Func g) {
    if (!u0) return new Tree(g);
    TY gL = g(l), gR = g(r);
    for (Tree u = u0; ; ) {
      TY fL = u.f ? u.f(l) : TY.min, fR = u.f ? u.f(r) : TY.min;
      if (fL >= gL && fR >= gR) return u0;
      if (fL <= gL && fR <= gR) { u.f = g; return u0; }
      if (r - l == 1) { if (fL <= gL) { u.f = g; } return u0; }
      const mid = l + (r - l) / 2;
      TY fMid = u.f(mid), gMid = g(mid);
      if (fMid < gMid) {
        swap(u.f, g);
        if (!g) return u0;
        if (gL < fL) {
          if (!u.l) { u.l = new Tree(g); return u0; }
          u = u.l; r = mid; gL = fL; gR = fMid;
        } else {
          if (!u.r) { u.r = new Tree(g); return u0; }
          u = u.r; l = mid; gL = fMid; gR = fR;
        }
      } else {
        if (fL < gL) {
          if (!u.l) { u.l = new Tree(g); return u0; }
          u = u.l; r = mid; gR = gMid;
        } else {
          if (!u.r) { u.r = new Tree(g); return u0; }
          u = u.r; l = mid; gL = gMid;
        }
      }
    }
  }
  Tree add(Tree u, TX l, TX r, TX a, TX b, Func g) {
    if (b <= l || r <= a) return u;
    if (a <= l && r <= b) return add(u, l, r, g);
    if (u && u.f && u.f(l) >= g(l) && u.f(r) >= g(r)) return u;
    if (!u) u = new Tree(null);
    const mid = l + (r - l) / 2;
    u.l = add(u.l, l, mid, a, b, g);
    u.r = add(u.r, mid, r, a, b, g);
    return u;
  }
}

// y = p x + q
class Line {
  alias TX = long;
  alias TY = long;
  long p, q;
  this(long p, long q) {
    this.p = p;
    this.q = q;
  }
  TY opCall(TX x) {
    return p * x + q;
  }
}


enum INF = 10L^^18;

void main() {
  try {
    for (; ; ) {
      const N = readInt;
      const M = readInt;
      auto W = new long[N];
      foreach (u; 0 .. N) {
        W[u] = readLong;
      }
      auto A = new int[M];
      auto B = new int[M];
      auto C = new long[M];
      foreach (i; 0 .. M) {
        A[i] = readInt - 1;
        B[i] = readInt - 1;
        C[i] = readLong;
      }
      
      auto G = new int[][N];
      foreach (i; 0 .. M) {
        G[A[i]] ~= i;
        G[B[i]] ~= i;
      }
      
      long[][2] dist;
      foreach (h; 0 .. 2) {
        const src = (h == 0) ? 0 : (N - 1);
        alias Entry = Tuple!(long, "c", int, "u");
        BinaryHeap!(Array!Entry, "a.c > b.c") que;
        dist[h] = new long[N];
        dist[h][] = INF;
        que.insert(Entry(dist[h][src] = 0, src));
        for (; !que.empty; ) {
          const c = que.front.c;
          const u = que.front.u;
          que.removeFront;
          if (dist[h][u] == c) {
            foreach (i; G[u]) {
              const cc = c + C[i];
              const v = A[i] ^ B[i] ^ u;
              if (chmin(dist[h][v], cc)) {
                que.insert(Entry(cc, v));
              }
            }
          }
        }
        debug {
          writeln(src, " ", dist[h]);
        }
      }
      
      long ans = dist[1][0];
      auto lct = new LiChaoTree!Line(W.minElement, W.maxElement + 1);
      foreach (u; 0 .. N) {
        lct.add(new Line(-W[u], -dist[0][u]));
      }
      foreach (u; 0 .. N) {
        chmin(ans, dist[1][u] - lct(W[u]));
      }
      writeln(ans);
    }
  } catch (EOFException e) {
  }
}