#include <bits/stdc++.h>
using namespace std;
#define mp make_pair
#define pb push_back
#define fi first
#define se second
int read(){
char p;
while((p = getchar_unlocked())){
if(p < '0' || p > '9') continue;
break;
}
int ret = p - '0';
while((p = getchar_unlocked())){
if(p >= '0' && p <= '9'){
ret *= 10;
ret += p - '0';
}
else break;
}
return ret;
}
int n, m, u, v;
int s, d, a, b, disa[200007], disb[200007], dist[200007];
bool vis[200007];
queue <int> q;
vector <int> edge[200007];
int go(int st){
memset(dist, 0, sizeof(dist));
memset(vis, false, sizeof(vis));
int res = 0;
q.push(st);
vis[st] = true;
while(!q.empty()){
u = q.front();
q.pop();
res = max(res, dist[u]);
for(int v : edge[u]){
if(vis[v]) continue;
if(disa[u] == disa[v] + 1 && disb[u] == disb[v] + 1){
vis[v] = true;
dist[v] = dist[u] + 1;
q.push(v);
}
}
}
return res;
}
int main(){
n = read(), m = read();
s = read(), d = read(), a = read(), b = read();
for(int i = 1; i <= m; i++){
u = read();
v = read();
edge[u].pb(v);
edge[v].pb(u);
}
vis[a] = true;
q.push(a);
while(!q.empty()){
u = q.front();
q.pop();
for(int v : edge[u]){
if(vis[v]) continue;
vis[v] = true;
disa[v] = disa[u] + 1;
q.push(v);
}
}
memset(vis, false, sizeof(vis));
vis[b] = true;
q.push(b);
while(!q.empty()){
u = q.front();
q.pop();
for(int v : edge[u]){
if(vis[v]) continue;
vis[v] = true;
disb[v] = disb[u] + 1;
q.push(v);
}
}
int cal_a = disa[d] - disa[s];
int cal_b = disb[d] - disb[s];
//cout << cal_a << " " << cal_b << endl;
if(min(cal_a, cal_b) < 0){
printf("-1");
return 0;
}
if(cal_a != cal_b){
cal_a = min(cal_a, cal_b);
cout << cal_a;
return 0;
}
int down_s = go(s), down_d = go(d);
if(cal_a + down_s < down_d) cal_a--;
if(cal_a < 0) cout << -1;
else cout << cal_a;
}
