//#pragma GCC optimize("O3")
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/rope>
#define mem(a,v) memset((a), (v), sizeof (a))
#define enl printf("\n")
#define case(t) printf("Case #%d: ", (t))
#define ni(n) scanf("%d", &(n))
#define nl(n) scanf("%lld", &(n))
#define nai(a, n) for (int i = 0; i < (n); i++) ni(a[i])
#define nal(a, n) for (int i = 0; i < (n); i++) nl(a[i])
#define pri(n) printf("%d\n", (n))
#define prl(n) printf("%lld\n", (n))
#define pii pair<int, int>
#define pil pair<int, long long>
#define pll pair<long long, long long>
#define vii vector<pii>
#define vil vector<pil>
#define vll vector<pll>
#define vi vector<int>
#define vl vector<long long>
#define pb push_back
#define mp make_pair
#define fi first
#define se second
using namespace std;
using namespace __gnu_pbds;
typedef long long ll;
typedef cc_hash_table<int,int,hash<int>> ht;
typedef tree<int,null_type,less<int>,rb_tree_tag,tree_order_statistics_node_update> oset;
const double pi = acos(-1);
const int MOD = 1e9 + 7;
const int INF = 1e9 + 7;
const int MAXN = 1e6 + 5;
const double eps = 1e-9;
int n, m, dp[MAXN];
vi adj[MAXN];
pii bfs(int src, int x, int y, int p = 0) {
deque<int> pq;
mem(dp, 0x3f);
dp[src] = 0;
dp[p] = 0;
pq.pb(src);
while (!pq.empty()) {
int u = pq.front(); pq.pop_front();
for (int v: adj[u]) {
if (dp[v] != 1061109567)
continue;
dp[v] = dp[u] + 1;
pq.pb(v);
}
}
return mp(dp[x], dp[y]);
}
int main() {
int s, d, a, b;
scanf("%d %d %d %d %d %d", &n, &m, &s, &d, &a, &b);
for (int i = 1; i <= m; i++) {
int u, v;
scanf("%d %d", &u, &v);
adj[u].pb(v);
adj[v].pb(u);
}
pii a1 = bfs(s, a, b);
pii a2 = bfs(d, a, b);
//cerr << a1.fi << "/" << a2.fi << " | " << a1.se << "/" << a2.se << "\n";
int ans = min(a2.fi - a1.fi, a2.se - a1.se);
if (a2.fi == a2.se && a1.fi == a1.se) {
pii a3 = bfs(d, a, b, s);
if (a2 == a3)
ans--;
}
if (ans < 0) ans = -1;
pri(ans);
return 0;
}
