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

int main() {
    int n, m, s, t, k;
    cin >> n >> m >> s >> t >> k;
    s--;
    t--;
    vector<vector<int>> g(n);
    for (int i = 0; i < m; i++) {
        int a, b;
        cin >> a >> b;
        a--;
        b--;
        g[a].push_back(b);
        g[b].push_back(a);
    }
    vector<int> dist(n, -1);
    queue<int> q;
    dist[s] = 0;
    q.push(s);
    while (!q.empty()) {
        int v = q.front();
        q.pop();
        for (int nv : g[v]) {
            if (dist[nv] != -1) {
                continue;
            }
            dist[nv] = dist[v] + 1;
            q.push(nv);
        }
    }
    if (abs(dist[t] - k) % 2 == 0) {
        if (dist[t] <= k) {
            cout << "Yes" << endl;
        } else {
            cout << "Unknown" << endl;
        }
    } else {
        cout << "No" << endl;
    }
}