import sys
input = lambda :sys.stdin.readline()[:-1]
ni = lambda :int(input())
na = lambda :list(map(int,input().split()))
yes = lambda :print("yes");Yes = lambda :print("Yes");YES = lambda : print("YES")
no = lambda :print("no");No = lambda :print("No");NO = lambda : print("NO")
#######################################################################

n, m = na()
s,t,k = na()
s -= 1
t -= 1

g = [[] for i in range(n)]
for i in range(m):
    a, b = na()
    g[a-1].append(b-1)
    g[b-1].append(a-1)

if n == 1:
    No()
    exit()

if n == 2:
    if s == t and m >= 1:
        if k % 2 == 0:
            Yes()
        else:
            No()
    elif s == t and m == 0:
        No()
    elif s != t and m >= 1:
        if k % 2:
            Yes()
        else:
            No()
    else:
        if k % 2:
            print("Unknown")
        else:
            No()
    exit()


from heapq import *
INF = 10**18
def dijkstra(g, s, n):
    dist = [INF]*n
    hq = [(0, s)]
    dist[s] = 0
    while hq:
        d, v = heappop(hq)
        if dist[v]!=d:
            continue
        for to in g[v]:
            c = 1
            if dist[v] + c < dist[to]:
                dist[to] = dist[v] + c
                heappush(hq, (dist[to], to))
    return dist

dist = dijkstra(g, s, n)

if s == t:
    if len(g[s]) == 0:
        No()
    else:
        if k % 2:
            Yes()
        else:
            No()
    exit()


if dist[t] != INF and (dist[t]-k)%2:
    No()
    exit()
if dist[t] == INF:
    print("Unknown")
    exit()
if dist[t] <= k:
    Yes()
else:
    print("Unknown")