//Challenge: Accepted
#include <iostream>
#include <algorithm>
#include <vector>
#include <utility>
#include <queue>
#define ll long long
#define maxn 200005
#define pii pair<int, int>
#define ff first
#define ss second
#define io ios_base::sync_with_stdio(0);
using namespace std;
//#include <bits/extc++.h>
//using namespace __gnu_pbds;
//template<class T> using Tree = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_upate>;
vector<int> adj[maxn];
int d1[maxn], d2[maxn], d3[maxn], d4[maxn];
bool found[maxn];
void bfs(int n, int s, int dep[]) {
for (int i = 1;i <= n;i++) found[i] = false;
queue<int> que;
que.push(s);
dep[s] = 0;
while (que.size()) {
int cur = que.front();
que.pop();
found[cur] = 1;
for (int v:adj[cur]) {
if (!found[v]) {
found[v] = 1;
dep[v] = dep[cur] + 1;
que.push(v);
}
}
}
}
int main() {
io
int n, m;
cin >> n >> m;
int pa, pb, st, st2;
cin >> pa >> pb >> st >> st2;
for (int i = 0;i < m;i++) {
int u, v;
cin >> u >> v;
adj[u].push_back(v);
adj[v].push_back(u);
}
bfs(n, st, d1);
bfs(n, st2, d2);
bfs(n, pa, d3);
bfs(n, pb, d4);
if (d1[pa] == d2[pa] && d1[pb] == d2[pb]) {
int ans = d1[pb] - d1[pa];
int ma = 1<<30, mb = 1<<30;
for (int i = 1;i <= n;i++) {
if (d3[i] + d1[i] == d1[pa] && d1[i] == d2[i]) { //if on shortest path
ma = min(ma, d1[i]);
}
if (d4[i] + d1[i] == d1[pb] && d1[i] == d2[i]) {
mb = min(mb, d1[i]);
}
}
if (ma > mb) ans--;
cout << (ans >= 0 ? ans : -1) << "\n";
} else {
int ans = min(d1[pb] - d1[pa], d2[pb] - d2[pa]);
cout << (ans >= 0 ? ans : -1) << "\n";
}
}
/*
6 6
1 2 3 4
1 5
5 6
6 3
6 4
1 2
3 4
7 8
1 7 4 5
4 5
1 2
1 3
2 4
3 5
4 6
5 6
6 7
*/
