#include <bits/stdc++.h>
#define F first
#define S second
#define PB push_back
#define MP make_pair
#define EB emplace_back
#define V vector
#define ALL(v) (v).begin(), (v).end()
#define debug(x) cerr << "LINE(" << __LINE__ << ") ->" << #x << " is " << x << endl
using namespace std;
typedef long long ll;
typedef pair<int, int> pi;
typedef V<int> vi;
const int INF = 1e9 + 7, N = 2e5 + 7;
int da[N], db[N], ds[N], dd[N];
vi G[N];
void BFS(int s, int* d) {
d[s] = 0;
queue<int> q({s});
while(q.size()) {
int u = q.front(); q.pop();
for(int v:G[u]) if(d[v] == -1) {
d[v] = d[u] + 1;
q.push(v);
}
}
}
vi tt[N];
int dp[N];
signed main()
{
ios::sync_with_stdio(0), cin.tie(0);
memset(da, -1, sizeof da);
memset(db, -1, sizeof db);
memset(ds, -1, sizeof ds);
memset(dd, -1, sizeof dd);
int n, m;
cin >> n >> m;
int s, d, a, b;
cin >> s >> d >> a >> b;
for(int i = 0; i < m; i++) {
int u, v;
cin >> u >> v;
G[u].PB(v), G[v].PB(u);
}
BFS(a, da), BFS(b, db), BFS(s, ds), BFS(d, dd);
for(int i = 1; i <= n; i++) {
if(da[i] == db[i]) {
tt[da[i]].PB(i);
}
}
memset(dp, 0xc0, sizeof dp);
for(int i = 1; i <= n; i++) {
for(int j:tt[i]) {
dp[j] = 0;
for(int k:G[j]) if(da[k] == db[k] && da[k] == da[j] - 1)
dp[j] = max(dp[j], dp[k] + 1);
}
}
if(da[s] != db[s]) {
int can = min(da[d] - da[s], db[d] - db[s]);
if(can < 0) can = -1;
cout << can << '\n';
} else {
int need = INF;
for(int i = 1; i <= n; i++) {
if(da[i] < da[s] || db[i] < db[s]) {
need = min(need, dd[i]);
} else if(da[i] == da[s] && db[i] == db[s] && dp[i] > dp[s])
need = min(need, dd[i]);
}
cout << need - 1 << '\n';
}
}
