#include <bits/stdc++.h>
using namespace std;
const int N = 200005;
const int INF = 1e9;
int n, m;
int p0, p1, a[2];
int dis[2][N];
int f[N], dis2[N];
bool lose[N];
vector<int> G[N];
void bfs(int t) {
for (int i = 1; i <= n; ++i) dis[t][i] = INF;
queue<int> qu; dis[t][a[t]] = 0, qu.push(a[t]);
while (qu.size()) {
int u = qu.front(); qu.pop();
for (auto v : G[u]) {
if (dis[t][v] == INF) {
dis[t][v] = dis[t][u] + 1, qu.push(v);
}
}
}
}
void dfs(int u) {
f[u] = 1;
for (auto v : G[u]) {
if (dis[0][v] + 1 != dis[0][u] || dis[1][v] + 1 != dis[1][u]) continue;
if (!f[v]) dfs(v); f[u] = max(f[u], f[v] + 1);
}
}
int main() {
ios::sync_with_stdio(false);
cin >> n >> m;
cin >> p0 >> p1 >> a[0] >> a[1];
for (int i = 1; i <= m; ++i) {
int u, v; cin >> u >> v;
G[u].push_back(v), G[v].push_back(u);
}
bfs(0), bfs(1);
for (int i = 1; i <= n; ++i) {
if (dis[0][i] < dis[0][p0] || dis[1][i] < dis[1][p0]) lose[i] = 1;
}
if (dis[0][p0] == dis[1][p0]) {
for (int i = 1; i <= n; ++i) {
if (dis[0][i] == dis[0][p0] && dis[1][i] == dis[1][p0] && !f[i]) dfs(i);
}
for (int i = 1; i <= n; ++i) {
if (f[i] > f[p0]) lose[i] = 1;
}
}
for (int i = 1; i <= n; ++i) dis2[i] = -1;
queue<int> qu; dis2[p1] = 0, qu.push(p1);
while (qu.size()) {
int u = qu.front(); qu.pop();
if (lose[u]) {
cout << dis2[u] - 1; return 0;
}
for (auto v : G[u]) {
if (dis2[v] == -1) {
dis2[v] = dis2[u] + 1, qu.push(v);
}
}
}
}
