#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);
}
}
//cout << "pas: "; for(auto &x : pas) cout << x << " ";
//cout << endl;
bfs(pas, d1);
//cout << "tada d1[" << s1 << "] = " << d1[s1] << ", o d1[" << s2 << "] = " << d1[s2] << "\n";
bool ret = (d2[s1] <= d1[s1] && d2[s2] <= d1[s2]);
//cout << "can(" << wait << ") = " << ret << endl << endl;
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;
}
}
cout << max(ans-1, -1);
return 0;
}
/*
6 6
1 2 3 4
1 5
5 6
6 3
6 4
1 2
3 4
6 7
5 6 1 2
6 3
1 2
1 3
2 3
1 5
2 4
5 4
*/
