#include <stdio.h>
#include <vector>
#include <queue>
#include <set>
#include <map>
#include <algorithm>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <stack>
#include <ctype.h>
#define p(x,y) pair<x, y>
#define pii pair<int, int>
#define v(x) vector<x>
#define q(x) queue<x>
#define pq(x) priority_queue<x>
#define uppq(x, comp) priority_queue<x, vector<x>, comp>
#define st(x) set<x>
#define m(x, y) map<x, y>
#define fi(s,e) for(int i=s;i<e;i++)
#define fj(s,e) for(int j=s;j<e;j++)
#define fk(s,e) for(int k=s;k<e;k++)
typedef long long int ll;
typedef unsigned long long int ull;
typedef __int128 ulll;
using namespace std;
int n,m;
int s,d,a,b;
v(int) pushvec;
v(v(int)) vec;
int dista[200010], distb[200010];
int dpdiv[200010];
void spreada(int x){
q(int) qu;
qu.push(x);
dista[x]=0;
while(!qu.empty()){
int now = qu.front();
qu.pop();
int sz = vec[now].size();
fi(0,sz){
int next = vec[now][i];
if(dista[next]==-1){
dista[next]=dista[now]+1;
qu.push(next);
}
}
}
return;
}
void spreadb(int x){
q(int) qu;
qu.push(x);
distb[x]=0;
while(!qu.empty()){
int now = qu.front();
qu.pop();
int sz = vec[now].size();
fi(0,sz){
int next = vec[now][i];
if(distb[next]==-1){
distb[next]=distb[now]+1;
qu.push(next);
}
}
}
return;
}
int find(int now){
if(dpdiv[now]) return dpdiv[now];
int sz = vec[now].size();
int ans = dista[now];
fi(0,sz){
int next = vec[now][i];
if(dista[next]==dista[now]-1 && dista[next]==distb[next]){
ans = min(ans, find(next));
}
}
return dpdiv[now]=ans;
}
int main(void){
scanf("%d%d%d%d%d%d",&n,&m,&s,&d,&a,&b);
fi(0,n+1) vec.push_back(pushvec);
fi(0,m){
int s,e;
scanf("%d%d",&s,&e);
vec[s].push_back(e);
vec[e].push_back(s);
}
fi(1,n+1){
dista[i]=-1;
distb[i]=-1;
}
spreada(a);
spreadb(b);
int ans = min(dista[d]-dista[s], distb[d]-distb[s]);
if(dista[s]==distb[s] && distb[d]==distb[d]){
int divds, divdd;
divds = find(s);
divdd = find(d);
if(divds > divdd) ans--;
}
printf("%d\n", max(ans, -1));
return 0;
}
