#include <bits/stdc++.h>
using namespace std;
template<typename Ostream, typename Cont>
typename enable_if<is_same<Ostream, ostream>::value, Ostream&>::type operator<<(Ostream& os,  const Cont& v){
  os << "[ ";
	for(auto &x : v)
    os << x << ' ';
	return os << "]";
}
template<typename Ostream, typename ...Ts>
Ostream& operator << (Ostream &os, const pair<Ts...> &p){
  return os << "{" << p.first << ", " << p.second << "}";
}
void dbg_cerr() { cerr << "\e[0m\n"; }
template<typename Head, typename... Tail> void dbg_cerr(Head H, Tail... T) { cerr << ' ' << H; dbg_cerr(T...); }
#ifdef LTF
#define DEBUG(...) cerr << "\e[1;31m[" #__VA_ARGS__ "]:", dbg_cerr(__VA_ARGS__)
#else
#define DEBUG(...)
#endif

void Solve() {
  int N, M; cin >> N >> M;
  int s, t, k; cin >> s >> t >> k;
  s--, t--;
  vector g(N, vector<int>());
  for (int i = 0; i < M; i++) {
    int x, y; cin >> x >> y;
    x--, y--;
    g[x].push_back(y), g[y].push_back(x);
  }

  if (N == 1) {
    assert(s == t);
    if (k == 0) cout << "Yes\n";
    else cout << "No\n";
    return;
  }

  vector<int> dis(N, -1);
  queue<int> q;
  dis[s] = 0, q.push(s);
  while (!q.empty()) {
    int u = q.front(); q.pop();
    for (int v : g[u]) {
      if (dis[v] == -1) {
        dis[v] = dis[u] + 1;
        q.push(v);
      }
    }
  }

  DEBUG(dis[t]);
  if (dis[t] == -1) {
    if (N == 2 && (k % 2 == 0)) {
      cout << "No\n";
    } else {
      cout << "Unknown\n";
    }
  } else {
    if ((dis[t] ^ k) & 1) {
      // dis and k have different parity
      cout << "No\n";
    } else {
      if (s == t) {
        if (k == 0) cout << "Yes\n";
        else {
          bool flag = true;
          for (int u = 0; u < N; u++) {
            if (u != s) flag &= (dis[u] == -1);
          }
          if (flag) cout << "Unknown\n";
          else cout << "Yes\n";
        }
      } else {
        if (dis[t] <= k) cout << "Yes\n";
        else cout << "Unknown\n";
      }
    }
  }
}

int main() {
  ios_base::sync_with_stdio(false); cin.tie(nullptr);
  int T = 1;
  // cin >> T;
  while (T--) {
    Solve();
  }
  return 0;
}