#include <bits/stdc++.h>
using namespace std;
using pii = pair<int, int>;
const int MAX_N = 2e5 + 5, INF = 1e9;
int n, m;
int a, b, tar1, tar2;
vector<int> adj[MAX_N];
int dist[MAX_N];
bool seen[MAX_N];
queue<int> order;
void bfs(int s) {
for (int i = 1; i <= n; i++) seen[i] = false;
seen[s] = true;
dist[s] = 0;
order.push(s);
while (order.size()) {
int u = order.front();
order.pop();
for (int v : adj[u]) {
if (seen[v]) continue;
seen[v] = true;
dist[v] = dist[u] + 1;
order.push(v);
}
}
}
int d[MAX_N][3];
int dp[MAX_N];
vector<pii> order2;
void precomp() {
bfs(tar1);
for (int i = 1; i <= n; i++) d[i][1] = dist[i];
bfs(tar2);
for (int i = 1; i <= n; i++) d[i][2] = dist[i];
for (int i = 1; i <= n; i++) {
if (d[i][1] != d[i][2]) continue;
order2.push_back({d[i][1], i});
}
sort(order2.begin(), order2.end());
for (pii el : order2) {
int u = el.second;
dp[u] = 1;
for (int v : adj[u]) {
if (!(d[v][1] == d[u][1] - 1 && d[v][2] == d[u][2] - 1)) continue;
dp[u] = max(dp[u], dp[v] + 1);
}
}
for (int i = 1; i <= n; i++) {
// cout << i << ": " << d[i][1] << " " << d[i][2] << endl;
// cout << i << ": " << dp[i] << endl;
}
}
bool does_b_win(int new_b) {
if (d[a][1] > d[new_b][1] || d[a][2] > d[new_b][2]) return true;
if (d[a][1] == d[new_b][1] && d[a][2] == d[new_b][2] && d[a][1] == d[a][2] && dp[a] < dp[new_b]) return true;
return false;
}
int main() {
// freopen("007.in", "r", stdin);
cin >> n >> m;
cin >> a >> b >> tar1 >> tar2;
for (int i = 1; i <= m; i++) {
int u, v; cin >> u >> v;
adj[u].push_back(v);
adj[v].push_back(u);
}
precomp();
bfs(b);
int ans = INF;
for (int i = 1; i <= n; i++) {
if (!does_b_win(i)) continue;
ans = min(ans, dist[i]);
}
ans--;
cout << ans << '\n';
}
