#include<bits/stdc++.h>
using namespace std;
#define pb push_back
#define fi first
#define se second
typedef pair<int, int> ii;
const int N = 2e5 + 5, inf = 1e9 + 123;
int n, m, src[2], a[2], d[2][N], l = -1, r = 6e5 + 5;
vector<int> gr[N];
void dijkstra (bool _) {
for (int i = 1; i <= n; ++i) d[_][i] = inf;
d[_][ src[_] ] = 0;
priority_queue<ii, vector<ii>, greater<ii> > pq; pq.push(ii(d[_][ src[_] ], src[_]) );
while (!pq.empty() ) {
ii tmp = pq.top(); pq.pop();
int u = tmp.se;
if (tmp.fi > d[_][u]) continue ;
for (int v : gr[u]) {
if (d[_][v] > d[_][u] + 1) {
d[_][v] = d[_][u] + 1;
pq.push(ii(d[_][v], v) );
}
}
}
}
bool check (int Time) {
d[1][ a[0] ] -= Time;
d[1][ a[1] ] -= Time;
if (d[0][ a[0] ] > d[1][ a[0] ] || d[0][ a[1] ] > d[1][ a[1] ]) {
d[1][ a[0] ] += Time;
d[1][ a[1] ] += Time;
return false;
}
d[1][ a[0] ] += Time;
d[1][ a[1] ] += Time;
return true;
}
int main () {
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
// freopen("SPY.INP", "r", stdin);
// freopen("SPY.OUT", "w", stdout);
cin >> n >> m;
cin >> src[0] >> src[1] >> a[0] >> a[1];
while (m --) {
int u, v; cin >> u >> v;
gr[u].pb(v); gr[v].pb(u);
}
dijkstra(0);
dijkstra(1);
while (l < r) {
int mid = (l + r + 1) / 2;
if (check(mid) ) l = mid;
else r = mid - 1;
}
cout << l;
return 0;
}
