#include <bits/stdc++.h>
using namespace std;
#define rep(i , j , k) for (int i = j; i < (int)k; i++)
#define pb push_back
#define mt make_tuple
#define for_all(x) x.begin(),x.end()
typedef long long ll;
typedef pair<int , int> pii;
typedef pair<ll, ll> pll;
typedef vector<int> vi;
typedef long double ld;
typedef complex<ld> point;
inline void fileIO(string s) {
freopen((s + ".in").c_str(), "r", stdin);
freopen((s + ".out").c_str(), "w", stdout);
}
template<class T , class S>
inline bool smin(T &a, S b) { return (T)b < a ? a = b , 1 : 0; }
template<class T , class S>
inline bool smax(T &a, S b) { return a < (T)b ? a = b , 1 : 0; }
constexpr int N = 1e6 + 10;
constexpr int MOD = 1e9 + 7;
template<typename T>
inline T mod(T &v) { return v = (v % MOD + MOD) % MOD; }
template<typename S, typename T>
inline S add(S &l, T r) { return mod(l += r); }
ll po(ll v, ll u) { return u ? po(v * v % MOD , u >> 1) * (u & 1 ? v : 1) % MOD : 1; }
int n , m;
int s , t , a , b, dist[N];
vector<int> adj[N];
int L , R , Q[N];
void bfs(int so) {
memset(dist , -1, sizeof(dist));
dist[so] = 0;
L = 0, R = 1;
Q[0] = so;
while (L < R) {
int me = Q[L++];
for (auto e : adj[me])
if (!~dist[e]) {
dist[e] = dist[me] + 1;
Q[R++] = e;
}
}
}
int arr[N];
void dfs(int v, int col) {
arr[v] += col;
for (auto e : adj[v])
if (dist[e] + 1 == dist[v] && arr[e] < col)
dfs(e , col);
}
int main() {
ios::sync_with_stdio(0);
cin.tie(0); cout.tie(0);
#ifndef LOCAL
// fileIO("forbidden1");
#endif
cin >> n >> m >> s >> t >> a >> b;
rep(i , 0 , m) {
int u , v;
cin >> u >> v;
adj[u].pb(v);
adj[v].pb(u);
}
bfs(s);
int A = dist[a];
int B = dist[b];
dfs(a , 1);
dfs(b , 2);
int alpha = 0;
rep(i , 0 , n + 1)
if (arr[i] == 3)
smax(alpha , dist[i]);
bfs(t);
int C = dist[a];
int D = dist[b];
memset(arr , 0 , sizeof(arr));
dfs(a , 1);
dfs(b , 2);
int beta = 0;
rep(i , 0 , n + 1)
if (arr[i] == 3)
smax(beta , dist[i]);
int res = min(C - A , D - B);
if (res < 0) return cout << -1 << endl, 0;
if (A == B && C == D && (C - beta) < (A - alpha))
res--;
if (res < 0) res = -1;
cout << res << endl;
return 0;
}
