#include <bits/stdc++.h>
#define FOR(i, x, y) for (int i = x; i < y; i++)
typedef long long ll;
using namespace std;
vector<int> graph[200001];
int visited[200001], reachable[200001];
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
int n, m, s, d, a, b;
cin >> n >> m >> s >> d >> a >> b;
FOR(i, 0, m) {
int a, b;
cin >> a >> b;
graph[a].push_back(b);
graph[b].push_back(a);
}
memset(visited, -1, sizeof(visited));
queue<int> q;
visited[s] = 0;
q.push(s);
while (q.size()) {
int curr = q.front();
q.pop();
for (int i : graph[curr]) {
if (!(~visited[i])) {
q.push(i);
visited[i] = visited[curr] + 1;
}
}
}
int l = 0, r = 1000000;
while (l != r) {
int mid = (l + r + 1) / 2;
memset(reachable, -1, sizeof(reachable));
queue<int> q;
reachable[d] = 0;
q.push(d);
while (q.size()) {
int curr = q.front();
q.pop();
for (int i : graph[curr]) {
if (!(~reachable[i]) && reachable[curr] + 1 < visited[i] + mid) {
reachable[i] = reachable[curr] + 1;
q.push(i);
}
}
}
if (~reachable[a] || ~reachable[b]) r = mid - 1;
else l = mid;
}
memset(reachable, -1, sizeof(reachable));
reachable[d] = 0;
q.push(d);
while (q.size()) {
int curr = q.front();
q.pop();
for (int i : graph[curr]) {
if (!(~reachable[i]) && reachable[curr] + 1 < visited[i] + l) {
reachable[i] = reachable[curr] + 1;
q.push(i);
}
}
}
if (~reachable[a] || ~reachable[b]) cout << -1;
else cout << l;
return 0;
}
