#include <bits/stdc++.h>
#define MP make_pair
#define F first
#define PB push_back
#define S second
using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
const int maxn = 2e5 + 4;
vector <int> g[maxn];
int dis[maxn][2];
int h[maxn];
int maximal_path (int v) {
memset (h, -1, sizeof h);
int ret = 0;
queue <int> q;
q.push(v);
h[v] = 0;
while (!q.empty()) {
v = q.front();
q.pop();
ret = max (ret, h[v]);
for (auto u : g[v]) {
if (h[u] == -1 and dis[u][0] < dis[v][0] and dis[u][1] < dis[v][1]) {
h[u] = h[v] + 1;
q.push (u);
}
}
}
return ret;
}
void bfs (int src, bool wh) {
queue <int> q;
q.push(src);
dis[src][wh] = 0;
while (!q.empty()) {
int v = q.front();
q.pop();
for (auto u : g[v]) {
if (dis[u][wh] == -1) {
dis[u][wh] = dis[v][wh] + 1;
q.push(u);
}
}
}
}
int main (){
ios_base::sync_with_stdio(false);
int n, m;
cin >> n >> m;
int s, t, a, b;
cin >> s >> t >> a >> b;
for (int e = 0; e < m; e ++) {
int v, u;
cin >> v >> u;
g[v].PB(u);
g[u].PB(v);
}
memset (dis, -1, sizeof dis);
bfs (a, 0);
bfs (b, 1);
int ans;
if (dis[t][0] < dis[s][0])
ans = -1;
else
ans = dis[t][0] - dis[s][0];
if (dis[t][1] < dis[s][1])
ans = -1;
else
ans = min (ans, dis[t][1] - dis[s][1]);
if (ans == -1)
return cout << -1 << endl, 0;
if (dis[s][0] == dis[s][1] and maximal_path(t) > maximal_path(s) + ans)
ans --;
return cout << ans << endl, 0;
}
