import sys
from collections import deque

def main():
    input = sys.stdin.read().split()
    ptr = 0
    N = int(input[ptr])
    ptr += 1
    M = int(input[ptr])
    ptr += 1
    s = int(input[ptr])-1
    ptr += 1
    t = int(input[ptr])-1
    ptr += 1
    k = int(input[ptr])
    ptr += 1

    adj = [[] for _ in range(N)]
    for _ in range(M):
        a = int(input[ptr])-1
        ptr += 1
        b = int(input[ptr])-1
        ptr += 1
        adj[a].append(b)
        adj[b].append(a)

    color = [-1] * N
    component = [-1] * N
    comp_id = 0

    for i in range(N):
        if color[i] == -1:
            q = deque()
            q.append(i)
            color[i] = 0
            component[i] = comp_id
            while q:
                u = q.popleft()
                for v in adj[u]:
                    if color[v] == -1:
                        color[v] = color[u] ^ 1
                        component[v] = comp_id
                        q.append(v)
                    else:
                        if color[v] == color[u]:
                            pass
            comp_id += 1

    s_color = color[s]
    t_color = color[t]
    if (s_color == t_color) != (k % 2 == 0):
        print("No")
        return

    if component[s] != component[t]:
        print("Unknown")
        return

    visited = [-1] * N
    q = deque()
    q.append(s)
    visited[s] = 0
    while q:
        u = q.popleft()
        for v in adj[u]:
            if visited[v] == -1:
                visited[v] = visited[u] + 1
                q.append(v)
                if v == t:
                    break
        if visited[t] != -1:
            break

    L = visited[t]
    if L == -1:
        print("Unknown")
        return

    if k >= L:
        print("Yes")
    else:
        print("Unknown")

if __name__ == "__main__":
    main()