import java.io.BufferedReader; import java.io.InputStreamReader; import java.util.ArrayDeque; import java.util.ArrayList; import java.util.Arrays; import java.util.List; import java.util.Queue; public class Main { public static void main(String[] args) throws Exception { BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); String[] sa = br.readLine().split(" "); int n = Integer.parseInt(sa[0]); int m = Integer.parseInt(sa[1]); sa = br.readLine().split(" "); int s = Integer.parseInt(sa[0]) - 1; int t = Integer.parseInt(sa[1]) - 1; int k = Integer.parseInt(sa[2]); Node2[] arr = new Node2[n]; for (int i = 0; i < n; i++) { Node2 o = new Node2(); arr[i] = o; } UnionFind uf = new UnionFind(n); for (int i = 0; i < m; i++) { sa = br.readLine().split(" "); int a = Integer.parseInt(sa[0]) - 1; int b = Integer.parseInt(sa[1]) - 1; arr[a].nexts.add(b); arr[b].nexts.add(a); uf.union(a, b); } br.close(); Queue que = new ArrayDeque<>(); for (int i = 0; i < n; i++) { if (arr[i].grp == 0) { que.add(i); arr[i].grp = 1; while (!que.isEmpty()) { int cur = que.poll(); for (int next : arr[cur].nexts) { if (arr[next].grp == 0) { que.add(next); arr[next].grp = 3 - arr[cur].grp; } else if (arr[next].grp == arr[cur].grp) { // 二部グラフではない throw new RuntimeException(); } } } } } if (uf.same(s, t)) { if ((arr[s].grp == arr[t].grp) ^ (k % 2 == 1)) { int[] d = new int[n]; Arrays.fill(d, -1); d[s] = 0; que = new ArrayDeque<>(); que.add(s); while (!que.isEmpty()) { int cur = que.poll(); for (int next : arr[cur].nexts) { if (d[next] == -1) { que.add(next); d[next] = d[cur] + 1; } } } if (d[t] <= k) { if (n == 1) { System.out.println("No"); } else { if (d[t] == 0 && arr[t].nexts.isEmpty()) { System.out.println("Unknown"); } else { System.out.println("Yes"); } } } else { System.out.println("Unknown"); } } else { System.out.println("No"); } } else { if (n == 2 && k % 2 == 0) { System.out.println("No"); } else { System.out.println("Unknown"); } } } static class Node2 { int grp; Integer target; List nexts = new ArrayList<>(); } static class UnionFind { int[] parent, size; int num = 0; // 連結成分の数 UnionFind(int n) { parent = new int[n]; size = new int[n]; num = n; for (int i = 0; i < n; i++) { parent[i] = i; size[i] = 1; } } void union(int x, int y) { int px = find(x); int py = find(y); if (px != py) { parent[px] = py; size[py] += size[px]; num--; } } int find(int x) { if (parent[x] == x) { return x; } parent[x] = find(parent[x]); return parent[x]; } /** * xとyが同一連結成分か */ boolean same(int x, int y) { return find(x) == find(y); } /** * xを含む連結成分のサイズ */ int size(int x) { return size[find(x)]; } } }