from collections import deque

n,m=map(int,input().split())
s,t,k=map(int,input().split())
edge=[list(map(int,input().split())) for _ in range(m)]

E=[[] for _ in range(n+1)]
for u,v in edge:
  E[v].append(u)
  E[u].append(v)
  
D=[10**9]*(n+1)
P=[-1]*(n+1)
D[s],P[s]=0,0
q=deque([(s)])
while q:
  x=q.popleft()
  for e in E[x]:
    if D[x]+1<D[e]:
      P[e]=P[x]^1
      D[e]=D[x]+1
      q.append(e)
if n==1:exit(print("No"))
if s==t:
  if k%2==1:exit(print("No"))
  if 1<=len(E[s]):
    exit(print("Yes"))
  else:
    exit(print("Unknown"))

if P[t]==0:
  if k%2==1:
    print("No")
  else:
    if D[t]<=k:
      print("Yes")
    else:
      print("Unknown")
elif P[t]==1:
  if k%2==0:
    print("No")
  else:
    if D[t]<=k:
      print("Yes")
    else:
      print("Unknown")
else:
  if n==1:print("No")
  elif n==2:
    if s==t:
      if k%2==1:print("No")
      else:print("Unknown")
    else:#s!=t
      if k%2==0:print("No")
      else:print("Unknown")
  else:
    print("Unknown")