#include <bits/stdc++.h>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/assoc_container.hpp>
using namespace std;
using namespace __gnu_pbds;
typedef long long ll;
typedef long double ld;
typedef complex<ld> cd;
typedef pair<int, int> pi;
typedef pair<ll,ll> pl;
typedef pair<ld,ld> pd;
typedef vector<int> vi;
typedef vector<ld> vd;
typedef vector<ll> vl;
typedef vector<pi> vpi;
typedef vector<pl> vpl;
typedef vector<cd> vcd;
template <class T> using Tree = tree<T, null_type, less<T>, rb_tree_tag,tree_order_statistics_node_update>;
#define FOR(i, a, b) for (int i=a; i<(b); i++)
#define F0R(i, a) for (int i=0; i<(a); i++)
#define FORd(i,a,b) for (int i = (b)-1; i >= a; i--)
#define F0Rd(i,a) for (int i = (a)-1; i >= 0; i--)
#define sz(x) (int)(x).size()
#define mp make_pair
#define pb push_back
#define f first
#define s second
#define lb lower_bound
#define ub upper_bound
#define all(x) x.begin(), x.end()
const int MOD = 1000000007;
const ll INF = 1e18;
const int MX = 200001;
int n,m,s,d,a,b,split[MX];
vi adj[MX];
int dist[2][MX];
void genDist(int k) {
queue<int> q;
FOR(i,1,n+1) dist[k][i] = MOD;
if (k == 0) {
dist[k][a] = 0; q.push(a);
} else {
dist[k][b] = 0; q.push(b);
}
while (sz(q)) {
int x = q.front(); q.pop();
for (int i: adj[x]) if (dist[k][i] == MOD) {
dist[k][i] = dist[k][x]+1;
q.push(i);
}
}
}
void genSplit() {
vector<array<int,3>> v;
FOR(i,1,n+1) v.pb({dist[0][i],dist[1][i],i});
sort(all(v));
for (auto a: v) if (a[0] == a[1]) {
split[a[2]] = a[0];
for (auto x: adj[a[2]])
if (dist[0][x] == dist[1][x] && dist[0][x] < a[0])
split[a[2]] = min(split[a[2]],split[x]);
}
}
int main() {
ios_base::sync_with_stdio(0); cin.tie(0);
cin >> n >> m;
cin >> s >> d >> a >> b;
F0R(i,m) {
int x,y; cin >> x >> y;
adj[x].pb(y), adj[y].pb(x);
}
genDist(0), genDist(1);
genSplit();
int ans = min(dist[0][d]-dist[0][s],dist[1][d]-dist[1][s]);
if (dist[0][d] == dist[1][d] && dist[0][s] == dist[1][s])
if (split[d] < split[s]) ans --;
cout << max(ans,-1);
// if equally close to one server, who wins?
// if equally close to both servers, who wins?
}
/* Look for:
* the exact constraints (multiple sets are too slow for n=10^6 :( )
* special cases (n=1?)
* overflow (ll vs int?)
* array bounds
*/
