#include <bits/stdc++.h>
using namespace std;
#define lli long long int
#define mp make_pair
#define eb emplace_back
#define pb push_back
#define pii pair<int,int>
#define pll pair<lli,lli>
#define X first
#define Y second
#define test(x) cout << #x << ' ' << x << endl
#define printv(x) { \
for (auto a : x) cout << a << endl; \
cout << endl;\
}
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
const int N = 300000, abc = 864197532, Doludu = 123;
vector <int> adj[N];
int dist[N], disa[N], disb[N], s, t, a, b, n;
bool chk(int d) {
int mna = 1 << 30, mnb = 1 << 30;
for (int i = 0; i < n; ++i) if (dist[i] <= d) mna = min(mna, disa[i]), mnb = min(mnb, disb[i]);
if (mna < disa[s]) return false;
if (mnb < disb[s]) return false;
return true;
}
int main () {
ios::sync_with_stdio(false);
cin.tie(0);
int m;
cin >> n >> m >> s >> t >> a >> b, --s, --t, --a, --b;
for (int i = 0, u, v; i < m; ++i) {
cin >> u >> v, --u, --v;
adj[u].pb(v);
adj[v].pb(u);
}
for (int i = 0; i < n; ++i) dist[i] = -1;
dist[t] = 0;
queue <int> q;
q.push(t);
while (!q.empty()) {
int v = q.front(); q.pop();
for (int u : adj[v]) if (dist[u] == -1) {
dist[u] = dist[v] + 1;
q.push(u);
}
}
for (int i = 0; i < n; ++i) disa[i] = -1;
disa[a] = 0;
q.push(a);
while (!q.empty()) {
int v = q.front(); q.pop();
for (int u : adj[v]) if (disa[u] == -1) {
disa[u] = disa[v] + 1;
q.push(u);
}
}
for (int i = 0; i < n; ++i) disb[i] = -1;
disb[b] = 0;
q.push(b);
while (!q.empty()) {
int v = q.front(); q.pop();
for (int u : adj[v]) if (disb[u] == -1) {
disb[u] = disb[v] + 1;
q.push(u);
}
}
if (!chk(0)) {
cout << -1 << endl;
} else {
int l = 0, r = n + 1;
while (r - l > 1) {
int mid = l + r >> 1;
if (chk(mid)) l = mid;
else r = mid;
}
cout << l << endl;
}
}
