#define DEBUG 0
#include <bits/stdc++.h>
using namespace std;
#if DEBUG
// basic debugging macros
int __i__,__j__;
#define printLine(l) for(__i__=0;__i__<l;__i__++){cout<<"-";}cout<<endl
#define printLine2(l,c) for(__i__=0;__i__<l;__i__++){cout<<c;}cout<<endl
#define printVar(n) cout<<#n<<": "<<n<<endl
#define printArr(a,l) cout<<#a<<": ";for(__i__=0;__i__<l;__i__++){cout<<a[__i__]<<" ";}cout<<endl
#define print2dArr(a,r,c) cout<<#a<<":\n";for(__i__=0;__i__<r;__i__++){for(__j__=0;__j__<c;__j__++){cout<<a[__i__][__j__]<<" ";}cout<<endl;}
#define print2dArr2(a,r,c,l) cout<<#a<<":\n";for(__i__=0;__i__<r;__i__++){for(__j__=0;__j__<c;__j__++){cout<<setw(l)<<setfill(' ')<<a[__i__][__j__]<<" ";}cout<<endl;}
// advanced debugging class
// debug 1,2,'A',"test";
class _Debug {
public:
template<typename T>
_Debug& operator,(T val) {
cout << val << endl;
return *this;
}
};
#define debug _Debug(),
#else
#define printLine(l)
#define printLine2(l,c)
#define printVar(n)
#define printArr(a,l)
#define print2dArr(a,r,c)
#define print2dArr2(a,r,c,l)
#define debug
#endif
// define
#define MAX_VAL 999999999
#define MAX_VAL_2 999999999999999999LL
#define EPS 1e-6
#define mp make_pair
#define pb push_back
// typedef
typedef unsigned int UI;
typedef long long int LLI;
typedef unsigned long long int ULLI;
typedef unsigned short int US;
typedef pair<int,int> pii;
typedef pair<LLI,LLI> plli;
typedef vector<int> vi;
typedef vector<LLI> vlli;
typedef vector<pii> vpii;
typedef vector<plli> vplli;
// ---------- END OF TEMPLATE ----------
vi adjList[200000];
int dist1[200000],dist2[200000];
int visited[200000],m;
int doDFS(int u) {
if (visited[u]) return 0;
int i;
visited[u] = 1;
m = min(m,dist1[u]);
for (i = 0; i < adjList[u].size(); i++) {
int v = adjList[u][i];
if ((dist1[v] == dist2[v]) && (dist1[v] < dist1[u])) doDFS(v);
}
return 0;
}
queue<int> Q;
int main() {
int i;
int N,M;
int s,d,a,b,u,v;
scanf("%d %d",&N,&M);
scanf("%d %d %d %d",&s,&d,&a,&b);
s--,d--,a--,b--;
for (i = 0; i < M; i++) {
scanf("%d %d",&u,&v);
u--,v--;
adjList[u].pb(v);
adjList[v].pb(u);
}
fill(dist1,dist1+N,-1);
dist1[a] = 0;
Q.push(a);
while (!Q.empty()) {
u = Q.front();
Q.pop();
for (i = 0; i < adjList[u].size(); i++) {
v = adjList[u][i];
if (dist1[v] == -1) {
dist1[v] = dist1[u]+1;
Q.push(v);
}
}
}
fill(dist2,dist2+N,-1);
dist2[b] = 0;
Q.push(b);
while (!Q.empty()) {
u = Q.front();
Q.pop();
for (i = 0; i < adjList[u].size(); i++) {
v = adjList[u][i];
if (dist2[v] == -1) {
dist2[v] = dist2[u]+1;
Q.push(v);
}
}
}
int ans = max(min(dist1[d]-dist1[s],dist2[d]-dist2[s]),-1);
if ((dist1[s] != dist2[s]) || (dist1[d] != dist2[d])) printf("%d\n",ans);
else {
m = N,doDFS(s);
int t = m;
if (!visited[d]) {
m = N,doDFS(d);
if (m < t) ans--;
}
printf("%d\n",max(ans,-1));
}
return 0;
}
