#include <bits/stdc++.h>
using namespace std;
const int dydis = 2e5 + 10;
const int inf = 1e9;
int n, m;
int s1, s2;
int gd, bd;
vector<int> gr[dydis];
int d1[dydis];
int d2[dydis];
void bfs(vector<int> start, int dist[]){
for(int i = 1; i <= n; i++) {
dist[i] = inf;
}
queue<int> q;
for(auto &x : start) {
q.push(x);
dist[x] = 0;
}
while(q.size()) {
int v = q.front();
q.pop();
for(auto &x : gr[v]) {
if(dist[x] > dist[v] + 1) {
dist[x] = dist[v] + 1;
q.push(x);
}
}
}
}
bool can(int wait) {
bfs({bd}, d1);
vector<int> pas;
for(int i = 1; i <= n; i++) {
if(d1[i] <= wait) {
pas.push_back(i);
}
}
bfs(pas, d1);
bool ret = (d2[s1] <= d1[s1] && d2[s2] <= d1[s2]);
return ret;
}
int dp1[dydis] = {};
int dp2[dydis] = {};
int when(int dist[]){
vector<pair<int, int> > vec;
for(int i = 1; i <= n; i++) {
vec.push_back({dist[i], i});
}
sort(vec.begin(), vec.end());
reverse(vec.begin(), vec.end());
int ret = 0;
for(int i = 0; i < n; i++) {
int v = vec[i].second;
dp1[v] = (v == s1);
dp2[v] = (v == s2);
for(auto x : gr[v]) {
if(dist[x] != dist[v] + 1) continue;
dp1[v] |= dp1[x];
dp2[v] |= dp2[x];
}
if(dp1[v] && dp2[v]) ret = max(ret, dist[v]);
}
return ret;
}
int main () {
cin.tie(NULL);
ios_base::sync_with_stdio(false);
cin >> n >> m;
cin >> gd >> bd >> s1 >> s2;
for(int i = 0; i < m; i++) {
int a, b; cin >> a >> b;
gr[a].push_back(b);
gr[b].push_back(a);
}
bfs({gd}, d2);
int l = 0, mid; int r = n; int ans = -1;
while(l <= r){
mid = (l + r) / 2;
if(can(mid)) {
ans = mid;
l = mid+1;
}else {
r = mid-1;
}
}
if(ans == -1) {
cout << ans;
return 0;
}
can(ans);
if(d1[s1] != d1[s2]) {
cout << ans;
return 0;
}
if(d2[s1] != d2[s2]) {
cout << ans;
return 0;
}
int kadaBlogas = when(d1);
int kadaGeras = when(d2);
ans -= (kadaGeras < kadaBlogas);
cout << ans;
return 0;
}
