#include<bits/stdc++.h>
using namespace std;
#define pb push_back
#define F first
#define S second
#define debug(x) cerr<<#x<<" :"<<x<<"\n"
#define all(x) x.begin(),x.end()
#define pii pair<int,int>
#define FAST ios_base::sync_with_stdio(false), cin.tie(), cout.tie();
//#define int long long
typedef long long ll;
typedef long double ld;
const int maxn = 2e5 + 7;
const int mod = 1e9 + 7;
const int INF = 1e9 + 7;
const int mlog = 20;
const int SQ = 400;
vector<int> adj[maxn];
int dis[4][maxn];
void bfs(int v,int dis[maxn])
{
for(int i = 0; i < maxn; i++) dis[i] = +INF;
dis[v] = 0;
queue<int> q; q.push(v);
while(!q.empty())
{
v = q.front(), q.pop();
for(int u : adj[v]) if(dis[v] + 1 < dis[u]) dis[u] = dis[v] + 1, q.push(u);
}
}
int32_t main()
{
FAST;
int n, m;
cin >> n >> m;
int s, d, a, b;
cin >> s >> d >> a >> b;
for(int i = 0;i < m; i++)
{
int u, v;
cin >> u >> v;
adj[u].pb(v), adj[v].pb(u);
}
bfs(d, dis[0]), bfs(s, dis[1]), bfs(a, dis[2]), bfs(b, dis[3]);
int dif1 = dis[0][a] - dis[1][a];
int dif2 = dis[0][b] - dis[1][b];
if(min(dif1, dif2) < 0) return cout << -1 << "\n", 0;
if(dif1 != dif2) return cout << min(dif1, dif2) << "\n", 0;
int mxS, mxD;
mxS = mxD = 0;
for(int i = 1; i <= n; i++) if(dis[0][i] + dis[2][i] == dis[0][a] && dis[0][i] + dis[3][i] == dis[0][b]) mxD = max(mxD, dis[0][i]);
for(int i = 1; i <= n; i++) if(dis[1][i] + dis[2][i] == dis[1][a] && dis[1][i] + dis[3][i] == dis[1][b]) mxS = max(mxS, dis[1][i]);
cout << dif1 - (dif1 + mxS < mxD) << "\n";
return 0;
}
