#include<bits/stdc++.h>
#define st first
#define nd second
#define pb push_back
#define ppb pop_back
#define ppf pop_front
#define umax(x,y) x=max(x,y)
#define umin(x,y) x=min(x,y)
#define ll long long
#define ii pair<int,int>
#define iii pair<ii,int>
#define iiii pair<ii,ii>
#define sz(x) ((int) x.size())
#define orta ((bas+son)/2)
#define all(x) x.begin(),x.end()
#define dbgs(x) cerr<<(#x)<<" --> "<<(x)<<" "
#define dbg(x) cerr<<(#x)<<" --> "<<(x)<<endl;getchar()
#define pw(x) (1ll<<(x))
#define inf 1000000000
#define MOD 1000000007
#define N 600005
#define M 1000003
#define LOG 16
#define KOK 650
#define EPS 0.00001
using namespace std;
int n,m,cur,cur0,s1,s2,x,y;
int dis[4][N],vis[N],vdag[2][N],dep[2][N],frb[N],nodes[2][N];
vector<int> v[N],dag[2][N];
void bfs(int start,int ar) {
queue<ii> q;
for(int i=1;i<=n;i++) vis[i]=0;
q.push({start,0});
while(!q.empty()) {
ii cur=q.front();
q.pop();
if(vis[cur.st]) continue ;
vis[cur.st]=1;
dis[ar][cur.st]=cur.nd;
for(int i:v[cur.st]) {
q.push({i,cur.nd+1});
}
}
}
bool ok(int wait) {
if(dis[1][s1]<dis[0][s1]+wait || dis[1][s2]<dis[0][s2]+wait) return false;
return true;
}
void fdag(int node,int w,int val,int ata) {
if(dis[2][node]!=val || dis[3][node]!=val) return ;
nodes[w][node]=1;
dag[w][ata].pb(node);
for(int i:v[node]) {
fdag(i,w,val-1,node);
}
}
int fdep(int node,int w) {
if(frb[node]) return 0;
if(vdag[w][node]) return dep[w][node];
dep[w][node]=1;
vdag[w][node]=1;
for(int i:dag[w][node]) {
// cout<<node<<" "<<i<<"\n";
umax(dep[w][node],fdep(i,w)+1);
}
return dep[w][node];
}
bool ok2(int val) {
fdag(cur0,0,min(dis[2][cur0],dis[3][cur0]),0);
fdag(cur,1,min(dis[2][cur],dis[3][cur]),0);
int dep0=fdep(0,0);
int dep1=fdep(0,1);
if(dep1+val>=dep0) return true;
for(int i=1;i<=n;i++) {
if(nodes[1][i]) frb[i]=1;
}
memset(vdag[0],0,sizeof(vdag[0]));
int dep0new=fdep(0,0);
if(dep0new!=dep0) return true;
return false;
}
int main() {
//freopen("input.txt","r",stdin);
ios_base::sync_with_stdio(0);
cin.tie(0);cout.tie(0);
cin>>n>>m;
cin>>cur>>cur0>>s1>>s2;
for(int i=1;i<=m;i++) {
cin>>x>>y;
v[x].pb(y);
v[y].pb(x);
}
bfs(cur,0);
bfs(cur0,1);
int bas=0,son=m;
while(bas<=son) {
if(ok(orta)) bas=orta+1;
else son=orta-1;
}
if(son==-1) {
cout<<-1;
return 0;
}
bfs(s1,2);
bfs(s2,3);
if(!ok2(son)) son--;
cout<<son;
}
