#include <bits/stdc++.h>
using namespace std;
const int mx = 2e5 + 5;
int n, m, s, v, a, b, dA[mx], dB[mx], ans; vector<int> adj[mx];
void bfs(int st, int *D){
queue<int> Q; fill(D, D + n + 1, -1);
Q.push(st); D[st] = 0;
while (!Q.empty()){
int i = Q.front(); Q.pop();
for (int j : adj[i]) if (D[j] == -1) D[j] = D[i] + 1, Q.push(j);
}
}
int nearer(int src){
queue<int> Q; int D[n + 1], ret = 0;
D[src] = 0; Q.push(src);
while (!Q.empty()){
int i = Q.front(); Q.pop();
ret = max(ret, D[i]);
for (int j : adj[i]) if (dA[j] < dA[i] and dB[j] < dB[i]) D[j] = D[i] + 1, Q.push(j);
}
return ret;
}
int main(){
cin >> n >> m >> s >> v >> a >> b;
for (int i = 1; i <= m; i++){
int a, b; cin >> a >> b;
adj[a].push_back(b); adj[b].push_back(a);
}
bfs(a, dA); bfs(b, dB);
int wA = dA[v] - dA[s], wB = dB[v] - dB[s];
if (wA == wB) ans = (nearer(s) >= nearer(v) - wA) ? wA : wA - 1;
else ans = min(wA, wB);
cout<<max(ans, -1)<<endl;
}
