#include <algorithm>
#include <iostream>
#include <vector>
using namespace std;
const int N = 200000;
vector<int> ej[N];
int dd0[N], dd1[N], dd[N], qu[N];
void bfs(int r, int *dd, int n) {
for (int i = 0; i < n; i++)
dd[i] = n;
int cnt = 0; dd[qu[cnt++] = r] = 0;
for (int h = 0; h < cnt; h++) {
int i = qu[h], d = dd[i] + 1;
for (int j : ej[i])
if (dd[j] == n)
dd[qu[cnt++] = j] = d;
}
}
int main() {
ios_base::sync_with_stdio(false), cin.tie(NULL);
int n, m; cin >> n >> m;
int t0, t1, s0, s1; cin >> t0 >> t1 >> s0 >> s1, t0--, t1--, s0--, s1--;
while (m--) {
int i, j; cin >> i >> j, i--, j--;
ej[i].push_back(j);
ej[j].push_back(i);
}
bfs(s0, dd0, n), bfs(s1, dd1, n);
if (dd0[t0] > dd1[t0])
for (int i = 0; i < n; i++)
swap(dd0[i], dd1[i]);
if (dd0[t0] < dd1[t0]) {
if (dd0[t1] < dd1[t1])
cout << max(dd0[t1] - dd0[t0], -1) << '\n';
else
cout << max(dd1[t1] - dd1[t0], -1) << '\n';
return 0;
}
if (dd0[t1] > dd1[t1])
for (int i = 0; i < n; i++)
swap(dd0[i], dd1[i]);
if (dd0[t1] < dd1[t1]) {
cout << max(dd0[t1] - dd0[t0], -1) << '\n';
return 0;
}
bfs(t0, dd, n);
int d0 = n;
for (int i = 0; i < n; i++)
if (dd0[i] == dd1[i] && dd0[i] + dd[i] == dd0[t0])
d0 = min(d0, dd0[i]);
bfs(t1, dd, n);
int d1 = n;
for (int i = 0; i < n; i++)
if (dd0[i] == dd1[i] && dd0[i] + dd[i] == dd0[t1])
d1 = min(d1, dd0[i]);
if (d0 <= d1)
cout << max(dd0[t1] - dd0[t0], -1) << '\n';
else
cout << max(dd0[t1] - dd0[t0] - 1, -1) << '\n';
return 0;
}
