from collections import deque
N, M = map(int, input().split())
s, t, k = map(int, input().split())
s -= 1
t -= 1
g = [[] for _ in range(N)]
for _ in range(M):
	u, v = map(int, input().split())
	u -= 1
	v -= 1
	g[u].append(v)
	g[v].append(u)
d = [10 ** 9] * N
d[s] = 0
q = deque([s])
while q:
	u = q.popleft()
	for v in g[u]:
		if d[u] + 1 < d[v]:
			d[v] = d[u] + 1
			q.append(v)
if d[t] < 10 ** 9:
	if d[t] % 2 == k % 2:
		print("Yes" if d[t] <= k else "Unknown")
	else:
		print("No")
else:
	if N == 2 and g[s] == [] and g[t] == [] and k % 2 == 0:
		print("No")
	else:
		print("Unknown")