//https://oj.uz/problem/view/CEOI14_007
#include<bits/stdc++.h>
const int N = 1e5 + 5;
using namespace std;
vector <int> G[N];
int n, m, p[2], a[2];
int d[2][N], d2[N], Max[N];
bool ck[N];
void bfs(int u, int t){
queue <int> mq; mq.push(u); d[t][u] = 1;
while (mq.size()){
u = mq.front(); mq.pop();
for (auto v : G[u]){
if (!d[t][v]){
d[t][v] = d[t][u] + 1;
mq.push(v);
}
}
}
}
void dfs(int u){
Max[u] = 1;
for (auto v : G[u]){
if (d[0][v] + 1 == d[0][u] && d[1][v] + 1 == d[1][u]){
if (!Max[v]) dfs(v);
Max[u] = max(Max[u], Max[v] + 1);
}
}
}
int main(){
ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);
cin >> n >> m;
cin >> p[0] >> p[1] >> a[0] >> a[1];
while (m--){
int u, v;
cin >> u >> v;
G[u].push_back(v);
G[v].push_back(u);
}
bfs(a[0], 0); bfs(a[1], 1);
for (int i = 1; i <= n; i++){
if (d[0][i] < d[0][p[0]] || d[1][i] < d[1][p[0]]) ck[i] = true;
}
if (d[0][p[0]] == d[1][p[0]]){
for (int i = 1; i <= n; i++){
if (d[0][i] == d[1][i] && d[0][i] == d[0][p[0]] && !Max[i]) dfs(i);
}
for (int i = 1; i <= n; i++) if (Max[i] > Max[p[0]]) ck[i] = true;
}
queue <int> mq; mq.push(p[1]); d2[p[1]] = 1;
while (mq.size()){
int u = mq.front(); mq.pop();
if (ck[u]) return cout << d2[u] - 2, 0;
for (auto v : G[u]){
if (!d2[v]){
d2[v] = d2[u] + 1;
mq.push(v);
}
}
}
}
