#include <iostream>
#include <vector>
#include <algorithm>
#include <cstdio>
#include <cmath>
#include <cstring>
#include <string>
#include <cassert>
#include <climits>
#include <fstream>
#include <stack>
#include <queue>
#include <map>
using namespace std;
const string FILE_NAME = "spy";
const string IN_FILE = FILE_NAME + ".inp";
const string OUT_FILE = FILE_NAME + ".out";
int readInt()
{
char ch = getchar(); int ans = 0, sgn = 1;
while (ch == ' ' || ch == '\n') ch = getchar();
if (ch == '-') sgn = -1, ch = getchar();
while (47 < ch && ch < 58) ans = ans * 10 + ch - 48, ch = getchar();
return ans * sgn;
}
const int INF = 1e8;
const int MAX = 200010;
int n, m;
int s, d, a, b;
vector< vector<int> > dist(3, vector<int>(MAX, INF));
vector<int> deci(MAX, INF);
vector<int> gr[MAX];
int32_t main()
{
// freopen(IN_FILE.c_str(), "r", stdin);
// freopen(OUT_FILE.c_str(), "w", stdout);
n = readInt(); m = readInt();
s = readInt(); d = readInt(); a = readInt(); b = readInt();
for (int i = 0; i < m; ++i) {
int u = readInt(), v = readInt();
gr[u].push_back(v);
gr[v].push_back(u);
}
dist[0][a] = 0;
queue<int> qu; qu.push(a);
while (!qu.empty()) {
int u = qu.front(); qu.pop();
for (int v : gr[u]) {
if (dist[0][v] == INF) {
dist[0][v] = dist[0][u] + 1;
qu.push(v);
}
}
}
dist[1][b] = 0;
assert(qu.empty());
qu.push(b);
while (!qu.empty()) {
int u = qu.front(); qu.pop();
for (int v : gr[u]) {
if (dist[1][v] == INF) {
dist[1][v] = dist[1][u] + 1;
qu.push(v);
}
}
deci[u] = dist[1][u];
for (int v : gr[u]) {
if (dist[0][v] + 1 == dist[0][u] && dist[1][v] + 1 == dist[1][u]) {
deci[u] = min(deci[u], deci[v]);
}
}
}
// for (int i = 1; i <= n; ++i) cerr << deci[i] << endl;
dist[2][d] = 0;
assert(qu.empty());
qu.push(d);
while (!qu.empty()) {
int u = qu.front(); qu.pop();
for (int v : gr[u]) {
if (dist[2][v] == INF) {
dist[2][v] = dist[2][u] + 1;
qu.push(v);
}
}
}
int ans = INF;
for (int u = 1; u <= n; ++u) {
bool block;
if (dist[0][s] > dist[0][u]) block = 0;
else if (dist[1][s] > dist[1][u]) block = 0;
else if (dist[0][s] < dist[0][u]) block = 1;
else if (dist[1][s] < dist[1][u]) block = 1;
else if (deci[s] <= deci[u]) block = 1;
else block = 0;
if (u == d && (!block)) {
cout << -1;
return 0;
}
if (!block) {
ans = min(ans, dist[2][u] - 1);
}
}
cout << ans;
}
