// CEOI14_007
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
const int mod = 1000 * 1000 * 1000 + 7;
const int INF = 1e9 + 100;
const ll LINF = 1e18 + 100;
#ifdef DEBUG
#define dbg(x) cout << #x << " = " << (x) << endl << flush;
#define dbgr(s, f) { cout << #s << ": "; for (auto _ = (s); _ != (f); _++) cout << *_ << ' '; cout << endl << flush; }
#else
#define dbg(x) ;
#define dbgr(s, f) ;
#endif
#define FOR(i, a, b) for (int i = (a); i < (b); i++)
#define fast_io ios::sync_with_stdio(false); cin.tie(0); cout.tie(0);
#define all(x) (x).begin(), (x).end()
#define pb push_back
#define mp make_pair
#define fr first
#define sc second
#define endl '\n'
#define MAXN 200100
#define MAXE 600100
int n, m;
int s, d, a, b;
vector<int> adj[MAXN];
int h[3][MAXN];
bool mark[MAXN];
bool amark[2][MAXN], bmark[2][MAXN];
int ans;
void bfs(int r, int *h)
{
memset(mark, 0, sizeof(mark));
queue<int> q;
mark[r] = true;
q.push(r);
while (!q.empty())
{
int v = q.front(); q.pop();
for (int u : adj[v])
{
if (mark[u]) continue;
mark[u] = true;
h[u] = h[v] + 1;
q.push(u);
}
}
}
void findpars(int r, int *h, bool *mark)
{
queue<int> q;
q.push(r);
mark[r] = true;
while (!q.empty())
{
int v = q.front(); q.pop();
for (int u : adj[v])
{
if (mark[u] || h[u] >= h[v]) continue;
mark[u] = true;
q.push(u);
}
}
}
int32_t main(void)
{
fast_io;
cin >> n >> m;
cin >> s >> d >> a >> b;
FOR(i, 0, m)
{
int x, y;
cin >> x >> y;
adj[x].pb(y);
adj[y].pb(x);
}
bfs(a, h[1]);
bfs(b, h[2]);
if (h[1][s] > h[1][d] || h[2][s] > h[2][d]) return cout << "-1\n", 0;
ans = min(h[1][d] - h[1][s], h[2][d] - h[2][s]);
if (h[1][d] - h[1][s] != h[2][d] - h[2][s]) return cout << ans << endl, 0;
findpars(s, h[1], amark[0]);
findpars(s, h[2], bmark[0]);
findpars(d, h[1], amark[1]);
findpars(d, h[2], bmark[1]);
int spy = 0, doc = 0;
FOR(i, 1, n + 1)
{
if (amark[0][i] && bmark[0][i] && h[1][i] - h[1][s] == h[2][i] - h[2][s]) spy = max(spy, h[1][s] - h[1][i]);
if (amark[1][i] && bmark[1][i] && h[1][i] - h[1][d] == h[2][i] - h[2][d]) doc = max(doc, h[2][d] - h[2][i]);
}
if (spy + h[1][d] - h[1][s] < doc) ans--;
cout << ans << endl;
return 0;
}
