#include <atcoder/dsu>

#include <bits/stdc++.h>

using namespace std;
#define SZ(x) (int) (x).size()
#define REP(i, n) for(int i = 0; i < (n); i++)
#define FOR(i, a, b) for(auto i = (a); i < (b); i++)
#define For(i, a, b, c) \
	for(auto i = (a); i != (b); i += (c))
#define REPR(i, n) for(auto i = (n) -1; i >= 0; i--)
#define ALL(s) (s).begin(), (s).end()
#define so(V) sort(ALL(V))
#define rev(V) reverse(ALL(V))
#define uni(v) v.erase(unique(ALL(v)), (v).end())
#define eb emplace_back

typedef unsigned long long ull;
typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<bool> vb;
typedef vector<vi> vvi;
typedef vector<vll> vvll;
typedef pair<int, int> PI;
typedef pair<ll, ll> PL;
const double EPS = 1e-6;
const int MOD = 1e9 + 7;
const int INF = (1 << 30);
const ll LINF = 1e18;
const double math_PI = acos(-1);

template<typename T>
vector<T> make_v(size_t a) {
	return vector<T>(a);
}

template<typename T, typename... Ts>
auto make_v(size_t a, Ts... ts) {
	return vector<decltype(make_v<T>(ts...))>(
		a, make_v<T>(ts...));
}

template<typename T, typename V>
typename enable_if<is_class<T>::value == 0>::type fill_v(
	T& t, const V& v) {
	t = v;
}

template<typename T, typename V>
typename enable_if<is_class<T>::value != 0>::type fill_v(
	T& t, const V& v) {
	for(auto& e: t) fill_v(e, v);
}

template<class T>
bool chmax(T& a, const T& b) {
	if(a < b) {
		a = b;
		return true;
	}
	return false;
}

template<class T>
bool chmin(T& a, const T& b) {
	if(a > b) {
		a = b;
		return true;
	}
	return false;
}

template<typename S, typename T>
istream& operator>>(istream& is, pair<S, T>& p) {
	cin >> p.first >> p.second;
	return is;
}

template<typename T>
istream& operator>>(istream& is, vector<T>& vec) {
	for(T& x: vec) is >> x;
	return is;
}

template<typename T>
string join(vector<T>& vec, string splitter) {
	stringstream ss;
	REP(i, SZ(vec)) {
		if(i != 0) ss << splitter;
		ss << vec[i];
	}
	return ss.str();
}

template<typename T>
ostream& operator<<(ostream& os, vector<T>& vec) {
	os << join(vec, " ");
	return os;
}
using namespace atcoder;
template<class T = ll>
struct Edge {
public:
	int from, to;
	T cost;
	Edge() {
	}
	Edge(int _from, int _to, T _cost) {
		from = _from;
		to = _to;
		cost = _cost;
	}
};
template<class T = ll>
using Edges = vector<Edge<T>>;
template<class T = ll>
using Graph = vector<Edges<T>>;
vll dijkstra(int s, const Graph<ll>& G) {
	using P = pair<ll, int>;
	priority_queue<P, vector<P>, greater<>> que;
	vll D(SZ(G), LINF);
	D[s] = 0;
	que.push(P(0, s));
	while(!que.empty()) {
		P p = que.top();
		que.pop();
		int v = p.second;
		if(D[v] < p.first) continue;
		for(Edge e: G[v]) {
			if(D[e.to] > D[v] + e.cost) {
				D[e.to] = D[v] + e.cost;
				que.push(P(D[e.to], e.to));
			}
		}
	}
	return D;
}

int main() {
	cin.tie(nullptr);
	ios::sync_with_stdio(false);
	int N, M;
	cin >> N >> M;
	int s, t, k;
	cin >> s >> t >> k;
	s--;
	t--;
	Graph<> G(N);
	dsu D(N);
	REP(i, M) {
		int A, B;
		cin >> A >> B;
		A--;
		B--;
		G[A].eb(A, B, 1);
		G[B].eb(B, A, 1);
		D.merge(A, B);
	}
	int g = SZ(D.groups());
	if(N == 1) {
		cout << "No" << endl;
		return 0;
	}
	if(s == t) {
		if(k % 2 == 1) {
			if(g >= 2 && N >= 3) {
				cout << "Unknown" << endl;
			} else {
				cout << "No" << endl;
			}
			return 0;
		} else {
			if(SZ(G[s]) == 0) {
				cout << "Unknown" << endl;
			} else {
				cout << "Yes" << endl;
			}
		}
		return 0;
	}
	auto d = dijkstra(s, G);
	if(!D.same(s, t)) {
		if(D.size(s) == 1 && D.size(t) == 1) {
			if(k % 2 == 1) {
				cout << "Unknown" << endl;
			} else if(g >= 3) {
				cout << "Unknown" << endl;
			} else {
				cout << "No" << endl;
			}
		} else {
			cout << "Unknown" << endl;
		}
	} else if(d[t] % 2 != k % 2) {
		cout << "No" << endl;
	} else if(d[t] > k) {
		cout << "Unknown" << endl;
	} else {
		cout << "Yes" << endl;
	}
	return 0;
}