import sys
from collections import deque

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

    adj = [[] for _ in range(N)]
    for _ in range(M):
        a = int(input[idx])-1; idx +=1
        b = int(input[idx])-1; idx +=1
        adj[a].append(b)
        adj[b].append(a)
    
    # BFS to find shortest path and check connectivity
    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 visited[t] == -1:
        # s and t are in different components
        print("Unknown")
        return
    
    d = visited[t]
    if (d % 2) != (k % 2):
        print("No")
        return
    
    if k >= d:
        print("Yes")
    else:
        print("Unknown")

if __name__ == "__main__":
    main()