/* -*- coding: utf-8 -*-
 *
 * 3111.cc:  No.3111 Toll Optimization - yukicoder
 */

#include<cstdio>
#include<vector>
#include<queue>
#include<algorithm>
#include<utility>

using namespace std;

/* constant */

const int MAX_N = 100000;
const int MAX_M = 100000;
const int MAX_K = 4;
const int MAX_GN = MAX_N * MAX_K;
const long long LINF = 1LL << 62;

/* typedef */

using ll = long long;
using pii = pair<int,int>;
using vpii = vector<pii>;
using pli = pair<ll,int>;

/* global variables */

int cs[MAX_M];
vpii nbrs[MAX_N];
ll ds[MAX_GN];

/* subroutines */

/* main */

int main() {
  int n, m, k;
  scanf("%d%d%d", &n, &m, &k);
  for (int i = 0; i < m; i++) scanf("%d", cs + i);
  for (int i = 0; i < m; i++) {
    int u, v;
    scanf("%d%d", &u, &v);
    u--, v--;
    nbrs[u].push_back({v, cs[i]});
    nbrs[v].push_back({u, cs[i]});
  }

  int gn = n << 2;
  fill(ds, ds + gn, LINF);
  ds[0] = 0;
  priority_queue<pli> q;
  q.push({0, 0});

  while (! q.empty()) {
    auto [ud, u] = q.top(); q.pop();
    ud = -ud;
    if (ds[u] != ud) continue;

    int ui = (u >> 2), uk = (u & 3);
    if (ui == n - 1) continue;

    for (auto [vi, c]: nbrs[ui]) {
      int v = (vi << 2) | uk;
      ll vd = ud + c;
      if (ds[v] > vd) ds[v] = vd, q.push({-vd, v});

      if (uk < k) {
	int v = (vi << 2) | (uk + 1);
	if (ds[v] > ud) ds[v] = ud, q.push({-ud, v});
      }
    }
  }

  ll gd = *min_element(ds + ((n - 1) << 2), ds + (n << 2));
  printf("%lld\n", (gd < LINF) ? gd : -1LL);
  
  return 0;
}