#include<bits/stdc++.h>
#define ll int
#define pb push_back
#define mp make_pair
#define ld long double
#define F first
#define S second
#define pii pair<ll,ll>
using namespace :: std;
const ll mod=1e9+7;
const ll maxn=2e5+500;
const ll inf=1e5+900;
vector<ll> ger[maxn];
ll fs[maxn];
ll fd[maxn];
ll fa[maxn];
ll fb[maxn];
bool vis[maxn];
void bfs(ll a,ll* f){
queue<ll> qu;
memset(vis,0,sizeof vis);
qu.push(a);
vis[a]=1;
while(qu.size()){
ll v=qu.front();
qu.pop();
for(auto u:ger[v]){
if(!vis[u]){
vis[u]=1;
f[u]=f[v]+1;
qu.push(u);
}
}
}
}
bool is_ok(ll q,ll w,ll e,ll r){
if(e>=q){
if(e+r>w+q){
return 0;
}else{
return 1;
}
}else{
if(e+r+1>w+q){
return 0;
}else{
return 1;
}
}
}
pii find_new(ll mid,ll q,ll w){
if(q>=mid){
return mp(q-mid,w);
}
mid-=q;
q=0;
return mp(0,w-mid);
}
int main(){
ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
ll n,m;
cin>>n>>m;
ll s,d,a,b;
cin>>s>>d>>a>>b;
for(ll i=0;i<m;i++){
ll a,b;
cin>>a>>b;
ger[a].pb(b);
ger[b].pb(a);
}
bfs(s,fs);
bfs(d,fd);
bfs(a,fa);
bfs(b,fb);
if(fd[a]!=fd[b] || fs[a]!=fs[b]){
ll r1=fd[a];
ll r2=fd[b];
ll w1=fs[a];
ll w2=fs[b];
if(r1>r2){
swap(r1,r2);
swap(w1,w2);
}
ll ans=min(r1-w1,r2-w2);
if(ans<0){
ans=-1;
}
cout<<ans<<endl;
}else{
ll mxd=0;
for(ll i=1;i<=n;i++){
if(fd[i]+fa[i]==fd[a] && fd[i]+fb[i]==fd[a]){
mxd=max(mxd,fd[i]);
}
}
ll mxs=0;
for(ll i=1;i<=n;i++){
if(fs[i]+fa[i]==fs[a] && fs[i]+fb[i]==fs[b]){
mxs=max(mxs,fs[i]);
}
}
ll q=mxd;
ll w=fd[a]-mxd;
ll e=mxs;
ll r=fs[a]-mxs;
if(!is_ok(q,w,e,r)){
cout<<-1;
return 0;
}
ll s=0;
ll t=inf;
while(t-s>1){
ll mid=(s+t)/2;
pii tr=find_new(mid,q,w);
if(is_ok(tr.F,tr.S,e,r)){
s=mid;
}else{
t=mid;
}
}
cout<<s;
return 0;
}
}
