#include <bits/stdc++.h>
#pragma GCC optimize ("O2")
#pragma GCC optimize ("unroll-loops")
//#pragma GCC optimize("no-stack-protector,fast-math")
using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<pii, int> piii;
typedef pair<ll, ll> pll;
#define debug(x) cerr<<#x<<'='<<(x)<<endl;
#define debugp(x) cerr<<#x<<"= {"<<(x.first)<<", "<<(x.second)<<"}"<<endl;
#define debug2(x, y) cerr<<"{"<<#x<<", "<<#y<<"} = {"<<(x)<<", "<<(y)<<"}"<<endl;
#define debugv(v) {cerr<<#v<<" : ";for (auto x:v) cerr<<x<<' ';cerr<<endl;}
#define all(x) x.begin(), x.end()
#define pb push_back
#define kill(x) return cout<<x<<'\n', 0;
const ld eps=1e-7;
const int inf=1000000010;
const ll INF=10000000000000010LL;
const int mod = 1000000007;
const int MAXN = 200010, LOG=20;
int n, m, k, u, v, x, y, t, a, b, ans;
int dist[4][MAXN];
vector<int> G[MAXN];
queue<int> Q;
void BFS(int* dist, int src){
dist[src]=0;
Q.push(src);
while (Q.size()){
int v=Q.front();
Q.pop();
for (int u:G[v]) if (dist[v]+1<dist[u]){
dist[u]=dist[v]+1;
Q.push(u);
}
}
}
int main(){
ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);
//freopen("input.txt", "r", stdin);
//freopen("output.txt", "w", stdout);
memset(dist, 31, sizeof(dist));
cin>>n>>m>>k>>t>>a>>b;
while (m--){
cin>>u>>v;
G[u].pb(v);
G[v].pb(u);
}
BFS(dist[0], a);
BFS(dist[1], b);
BFS(dist[2], k);
BFS(dist[3], t);
int fk=inf, ft=inf;
if (dist[0][k]==dist[1][k]){
for (int v=1; v<=n; v++){
if (dist[0][v]==dist[1][v] && dist[0][v]+dist[2][v]==dist[0][k]) fk=min(fk, dist[0][v]);
}
}
if (dist[0][t]==dist[1][t]){
for (int v=1; v<=n; v++){
if (dist[0][v]==dist[1][v] && dist[0][v]+dist[3][v]==dist[0][t]) ft=min(ft, dist[0][v]);
}
}
int dt=min(dist[0][t], dist[1][t]), dk=min(dist[0][k], dist[1][k]);
ans=dt-dk;
if (fk==inf && ft==inf){
int optk=(dist[1][k]==dk);
int optt=(dist[1][t]==dt);
ans-=(optk!=optt);
}
else ans-=(fk>ft);
if (ans<0) ans=-1;
cout<<ans<<'\n';
return 0;
}
