package main

import . "fmt"
import . "os"
import bf "bufio"
import "container/heap"

func main() {
	rd:=bf.NewReader(Stdin)
	var n,m,k int
	Fscan(rd,&n,&m,&k)
	costs := make([]int, m)
	for i := range costs {
		Fscan(rd,&costs[i])
	}
	g := make([][]*Edge, (n+1)*(k+1))
	for _, c := range costs {
		var u,v int
		Fscan(rd,&u,&v)
		for i := 0; i <= k; i++ {
			g[u*(k+1)+i] = append(g[u*(k+1)+i], &Edge{v*(k+1)+i, c})
			g[v*(k+1)+i] = append(g[v*(k+1)+i], &Edge{u*(k+1)+i, c})
		}
		for i := 0; i < k; i++ {
			g[u*(k+1)+i] = append(g[u*(k+1)+i], &Edge{v*(k+1)+i+1, 0})
			g[v*(k+1)+i] = append(g[v*(k+1)+i], &Edge{u*(k+1)+i+1, 0})
		}
	}
	bests := make([]int, (n+1)*(k+1))
	for i := range bests {
		bests[i] = 1e15
	}
	pq := make(PQ, 0, (n+1)*(k+1))
	heap.Push(&pq, &Item{1*(k+1), 0})
	for pq.Len() > 0 {
		item := heap.Pop(&pq).(*Item)
		if item.cost > bests[item.id] {
			continue
		}
		for _, e := range g[item.id] {
			c := item.cost + e.cost
			if c < bests[e.to] {
				bests[e.to] = c
				heap.Push(&pq, &Item{e.to, c})
			}
		}
	}
	var ans int = 1e15
	for i := 0; i <= k; i++ {
		ans = min(ans, bests[n*(k+1)+i])
	}
	if ans == 1e15 {
		ans = -1
	}
	Println(ans)
}

type Edge struct {
	to, cost int
}

type Item struct {
	id, cost int
}

type PQ []*Item
func (pq PQ) Len() int { return len(pq) }
func (pq PQ) Less(i, j int) bool { return pq[i].cost < pq[j].cost }
func (pq PQ) Swap(i, j int) { pq[i], pq[j] = pq[j], pq[i] }
func (pq *PQ) Push(x any) {
	*pq = append(*pq, x.(*Item))
}
func (pq *PQ) Pop() any {
	old := *pq
	n := len(old)-1
	x := old[n]
	*pq = old[:n]
	return x
}