#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
const int N=2000000+5;
int n;
int m;
int s,d,a,b;
int di[2][N];
vector<int>g[N];
void build(int k,int go)
{
for(int j=0;j<N;j++)
{
di[k][j]=-1;
}
di[k][go]=0;
queue<int>q;
q.push(go);
while(!q.empty())
{
int nod=q.front();
q.pop();
for(auto &nou:g[nod])
{
if(di[k][nou]==-1)
{
di[k][nou]=1+di[k][nod];
q.push(nou);
}
}
}
}
int main()
{
// freopen("input","r",stdin);
// freopen("output","w",stdout);
cin>>n>>m;
cin>>s>>d>>a>>b;
for(int i=1;i<=m;i++)
{
int x,y;
cin>>x>>y;
g[x].push_back(y);
g[y].push_back(x);
}
build(0,s);
build(1,d);
int a1=di[0][a],a2=di[0][b];
int b1=di[1][a],b2=di[1][b];
int x1=b1-a1;
int x2=b2-a2;
int ans;
if(x1!=x2)
{
ans=min(x1,x2);
}
else
{
ans=x1-1;
}
if(ans<-1)
{
ans=-1;
}
cout<<ans<<"\n";
return 0;
}
/**
**/
