#include <queue>
#include <vector>
#include <iostream>
using namespace std;
vector<int> shortest_path(int src, vector<vector<int> > &G) {
int N = G.size();
vector<int> dist(N, -1);
queue<int> que;
que.push(src);
dist[src] = 0;
while (!que.empty()) {
int u = que.front(); que.pop();
for (int i : G[u]) {
if (dist[i] == -1) {
dist[i] = dist[u] + 1;
que.push(i);
}
}
}
return dist;
}
int main() {
cin.tie(0);
ios_base::sync_with_stdio(false);
int N, M;
cin >> N >> M;
int S, D, A, B;
cin >> S >> D >> A >> B; --S, --D, --A, --B;
vector<vector<int> > G(N);
for (int i = 0; i < M; ++i) {
int a, b;
cin >> a >> b; --a, --b;
G[a].push_back(b);
G[b].push_back(a);
}
vector<int> da = shortest_path(A, G);
vector<int> db = shortest_path(B, G);
int s1 = da[D] - da[S];
int s2 = db[D] - db[S];
int ans = max(s1, s2);
if (ans < 0) cout << -1 << endl;
else cout << ans << endl;
return 0;
}
