#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h>
#define rc(x) return cout<<x<<endl,0
#define pb push_back
#define mkp make_pair
#define in insert
#define er erase
#define fd find
#define fr first
#define sc second
typedef long long ll;
typedef long double ld;
const ll INF=0x3f3f3f3f3f3f3f3f;
const ll llinf=(1LL<<62);
const int inf=(1<<30);
const int nmax=2e5+50;
const int mod=1e9+7;
using namespace std;
int n,m,s[2],a[2],d[2][nmax],x,y,mn,i,j;
vector<int>g[nmax];
queue<pair<int,int> >q;
pair<int,int>p;
int main()
{
//freopen("sol.in","r",stdin);
//freopen("sol.out","w",stdout);
//mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
ios_base::sync_with_stdio(false);cin.tie(0);cerr.tie(0);cout.tie(0);
cin>>n>>m;
cin>>s[0]>>s[1]>>a[0]>>a[1];
while(m--)
{
cin>>x>>y;
g[x].pb(y);
g[y].pb(x);
}
for(j=0;j<2;j++)
{
for(i=1;i<=n;i++)d[j][i]=inf;
q.push(mkp(s[j],0));
d[j][s[j]]=0;
while(!q.empty())
{
p=q.front();
q.pop();
for(i=0;i<(int)g[p.fr].size();i++)
{
x=g[p.fr][i];
if(d[j][x]!=inf)continue;
d[j][x]=p.sc+1;
q.push(mkp(x,d[j][x]));
}
}
}
mn=inf;
for(i=0;i<2;i++)
{
x=a[i];
mn=min(mn,d[1][x]-d[0][x]);
}
if(mn<-1)mn=-1;
if(mn!=-1 && d[0][a[0]]==d[0][a[1]] && d[1][a[0]]==d[1][a[1]])mn--;
cout<<mn<<endl;
return 0;
}
