n,m,k=map(int,input().split())
e=[[] for _ in range(n*(k+1))]
c=list(map(int,input().split()))
for i in range(m):
  u,v=map(int,input().split())
  u-=1
  v-=1
  for j in range(k+1):
    e[n*j+u]+=[(n*j+v,c[i])]
    e[n*j+v]+=[(n*j+u,c[i])]
    if j+1<=k:
      e[n*j+u]+=[(n*(j+1)+v,0)]
      e[n*j+v]+=[(n*(j+1)+u,0)]
for i in range(n):
  for j in range(k):
    e[n*j+i]+=[(n*(j+1)+i,0)]
X=10**20
v=[X]*n*(k+1)
v[0]=0
q=[(v[0],0)]
from heapq import heappush,heappop
while len(q):
  sc,sp=heappop(q)
  if sc>v[sp]:
    continue
  for tp,c in e[sp]:
    tc=sc+c
    if v[tp]>tc:
      v[tp]=tc
      heappush(q,(v[tp],tp))
a=v[n*k+n-1]
print(a if a<X else -1)