#include <bits/stdc++.h>
using namespace std;
const int MAXN = 2e5+5;
int d1[MAXN],d2[MAXN];
vector<int> adj[MAXN];
bool vis[MAXN];
int N,M,S,T,A,B;
void bfs(int u, int *dist){
fill(dist+1,dist+N+1,-1);
queue<int> q; q.push(u); dist[u] = 0;
while(!q.empty()){
int uu = q.front(); q.pop();
for(auto v : adj[uu]){
if(dist[v] == -1){
dist[v] = dist[uu]+1;
q.push(v);
}
}
}
}
int bfs2(int u){
fill(vis+1,vis+N+1,false);
queue<int> q; q.push(u); vis[u] = true;
int ans = 0;
while(!q.empty()){
int uu = q.front(); q.pop();
ans = max(ans,d1[u]-d1[uu]);
for(auto v : adj[uu]){
if(!vis[v] && d1[v] == d1[uu]-1 && d2[v] == d2[uu]-1){
q.push(v);
vis[v] = true;
}
}
}
return ans;
}
int main()
{
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
cin >> N >> M >> S >> T >> A >> B;
for(int i = 0;i<M;++i){
int u,v; cin >> u >> v;
adj[u].push_back(v); adj[v].push_back(u);
}
bfs(A,d1); bfs(B,d2);
int ret1 = d1[T]-d1[S], ret2 = d2[T]-d2[S];
if(ret1 != ret2){
cout << max(min(ret1,ret2),-1) << "\n";
}
else{
int ans1 = bfs2(S), ans2 = bfs2(T);
//cout << ans1 << " " << ans2 << "\n";
if(ans1+ret1 < ans2){
cout << max(ret1-1,-1) << "\n";
}
else{
cout << max(ret1,-1) << "\n";
}
}
return 0;
}
