#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define pb emplace_back
#define AI(i) begin(i), end(i)
template<class T> bool chmin(T &a, T b) { return b < a && (a = b, true); }
template<class T> bool chmax(T &a, T b) { return a < b && (a = b, true); }
#ifdef KEV
#define DE(args...) kout("[ " + string(#args) + " ] = ", args)
void kout() { cerr << endl; }
template<class T, class ...U> void kout(T a, U ...b) { cerr << a << ' ', kout(b...); }
template<class T> void debug(T l, T r) { while (l != r) cerr << *l << " \n"[next(l)==r], ++l; }
#else
#define DE(...) 0
#define debug(...) 0
#endif
const int MAX_N = 200010, inf = 1e9;
int n, m, s, d, A, B;
vector<int> edge[MAX_N];
int diss[MAX_N], disd[MAX_N], disa[MAX_N], disb[MAX_N];
void get_dis(int s, int *dis) {
fill(dis, dis + n + 1, inf);
queue<int> q;
q.emplace(s); dis[s] = 0;
while (q.size()) {
int x = q.front(); q.pop();
for (int u : edge[x])
if (chmin(dis[u], dis[x] + 1))
q.emplace(u);
}
}
bool valid(int rest) {
auto test = [&](int x) {
int art = diss[x] + rest;
int ga = art + disa[x], gb = art + disb[x];
if (max(disa[x], disb[x]) > 1) return false;
int da = disd[A], db = disd[B];
if (min(disa[x], disb[x]) == 1) {
if (art < min(da, db)) return true;
return false;
}
if (ga <= da && gb <= db) return true;
return false;
};
for (int i = 1;i <= n;++i)
if (test(i)) return true;
return false;
}
int32_t main() {
ios_base::sync_with_stdio(0), cin.tie(0);
cin >> n >> m >> s >> d >> A >> B;
for (int a, b, i = 0;i < m;++i) {
cin >> a >> b;
DE(a, b);
edge[a].pb(b), edge[b].pb(a);
}
get_dis(s, diss), get_dis(d, disd);
get_dis(A, disa), get_dis(B, disb);
if (!valid(0)) return puts("-1"), 0;
cout << min(disd[A]-disa[A], disd[B]-disd[B]) << '\n';
return 0;
int l = 0, r = n, mid;
while (l < r) {
mid = l + r >> 1;
if (valid(mid+1))
l = mid + 1;
else
r = mid;
}
cout << l << '\n';
}
