#include <bits/stdc++.h>
using namespace std;

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

template<class T> ostream& operator << (ostream& os, const vector<T>& vec) {
    if(vec.empty()) return os;
    os << vec[0];
    for(auto it = vec.begin(); ++it != vec.end(); ) os << ' ' << *it;
    return os;
}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    int n, m, s, t, k;
    cin >> n >> m >> s >> t >> k;
    s--, t--;
    vector<vector<int>> g(n);
    queue<int> que;
    vector<int> dp(n, 1 << 30);
    for(int i = 0; i < m; i++){
        int u, v;
        cin >> u >> v;
        u--, v--;
        g[u].emplace_back(v);
        g[v].emplace_back(u);
    }
    que.emplace(s);
    dp[s] = 0;
    while(!que.empty()){
        int v = que.front();
        que.pop();
        for(auto &&u : g[v]){
            if(dp[v] + 1 >= dp[u]) continue;
            dp[u] = dp[v] + 1;
            que.emplace(u);
        }
    }
    if(n == 1){
        cout << "No\n";
        return 0;
    }
    if(dp[t] == (1 << 30)){
        if(n == 2){
            cout << (k % 2 == (s != t) ? "Unknown" : "No") << '\n';
            return 0;
        }
        cout << "Unknown" << '\n';
        return 0;
    }
    if(abs(dp[t] - k) & 1){
        cout << "No\n";
        return 0;
    }
    cout << "No\n";
    return 0;
    cout << (dp[t] <= k ? "Yes" : "Unknown") << '\n';
}