//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 dep[maxn];
bool found[maxn];
void bfs(int s) {
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(st);
//cout << dep[pb] << " " << dep[pa] << endl;
int ans = dep[pb] - dep[pa];
for (int i = 1;i <= n;i++) found[i] = 0;
bfs(st2);
//cout << dep[pb] << " " << dep[pa] << endl;
ans = min(ans, dep[pb] - dep[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
6 7
5 6 1 2
6 3
1 2
1 3
2 3
1 5
2 4
5 4
*/
