from collections import deque


N, M = map(int, input().split())
S, T, K = map(int, input().split())
S, T = S - 1, T - 1
G = [[] for _ in range(N)]
for _ in range(M):
    A, B = map(int, input().split())
    A, B = A - 1, B - 1
    G[A].append(B)
    G[B].append(A)

D = [10**9] * N
D[S] = 0
Q = deque()
Q.append(S)

while Q:
    now = Q.popleft()
    for nxt in G[now]:
        if D[nxt] > D[now] + 1:
            D[nxt] = D[now] + 1
            Q.append(nxt)

if D[T] == 10**9 or D[T] % 2 != K % 2:
    print("No")
elif D[T] <= K:
    print("Yes")
else:
    print("Unknown")