#include <bits/stdc++.h>
using namespace std;
int main()
{
ios::sync_with_stdio(false);
cin.tie(0);
int n,m,s,d,a,b;
cin >> n >> m >> s >> d >> a >> b;
vector<vector<int> > graph(n+1,vector<int>());
for(int i = 0; i < m; i++) {
int x,y;
cin >> x >> y;
graph[x].push_back(y);
graph[y].push_back(x);
}
vector<bool> wass(n+1,false);
vector<int> dists(n+1,0);
vector<bool> wasd(n+1,false);
vector<int> distd(n+1,0);
wass[s] = true;
queue<int> q;
q.push(s);
while(!q.empty()) {
int v = q.front();
q.pop();
for(int u : graph[v]) {
if(!wass[u]) {
wass[u] = true;
q.push(u);
dists[u] = dists[v]+1;
}
}
}
wasd[d] = true;
q.push(d);
while(!q.empty()) {
int v = q.front();
q.pop();
for(int u : graph[v]) {
if(!wasd[u]) {
wasd[u] = true;
q.push(u);
distd[u] = distd[v]+1;
}
}
}
cout << max(min(distd[a]-dists[a],distd[b]-dists[b])-1,-1);
return 0;
}
