#include <bits/stdc++.h>
#define all(i) (i).begin(), (i).end()
#define debug(x) cerr << "Line(" << __LINE__ << ") -> " << #x << " is " << x << endl
using namespace std;
template<typename T1, typename T2>
ostream& operator << (ostream &i, pair<T1, T2> j) {
return i << j.first << ' ' << j.second;
}
template<typename T>
ostream& operator << (ostream &i, vector<T> j) {
i << '{' << j.size() << ':';
for (T ii : j) i << ' ' << ii;
return i << '}';
}
typedef long long ll;
typedef pair<int, int> pi;
int main() {
ios::sync_with_stdio(0), cin.tie(0);
int n, m, s, d, a, b;
cin >> n >> m >> s >> d >> a >> b;
--s, --d, --a, --b;
vector<int> g[n];
for (int i = 0; i < m; ++i) {
int x, y;
cin >> x >> y;
--x, --y;
g[x].push_back(y), g[y].push_back(x);
}
vector<int> disd(n, -1), diss(n, -1), disa(n, -1), disb(n, -1);
queue<int> q;
disd[d] = 0, q.push(d);
while (!q.empty()) {
int i = q.front();
q.pop();
for (int j : g[i]) if (disd[j] == -1)
disd[j] = disd[i] + 1, q.push(j);
}
diss[s] = 0, q.push(s);
while (!q.empty()) {
int i = q.front();
q.pop();
for (int j : g[i]) if (diss[j] == -1)
diss[j] = diss[i] + 1, q.push(j);
}
if (disd[a] != disd[b]) {
if (disd[a] < disd[b]) cout << max(disd[a] - diss[a], -1);
else cout << max(disd[b] - diss[b], -1);
}
else {
int tmp = max(disd[a] - 1 - diss[a], disd[b] - 1 - diss[b]);
vector<int> disa(n, -1), disb(n, -1);
disa[a] = 0, q.push(a);
while (!q.empty()) {
int i = q.front();
q.pop();
for (int j : g[i]) if (disa[j] == -1)
disa[j] = disa[i] + 1, q.push(j);
}
disb[b] = 0, q.push(b);
while (!q.empty()) {
int i = q.front();
q.pop();
for (int j : g[i]) if (disb[j] == -1)
disb[j] = disb[i] + 1, q.push(j);
}
int x = d;
for (int i = 0; i < n; ++i)
if (disa[i] == disb[i] && disd[i] + disa[i] == disd[a] && disa[i] < disa[x])
x = i;
for (int i = 0; i < n; ++i) if (disa[i] <= disa[x] && disb[i] <= disb[x])
tmp = max(tmp, disd[x] - diss[i] + disa[x] - max(disa[i], disb[i]));
cout << max(tmp, -1);
}
}
