#include<bits/stdc++.h>
using namespace std;
#define int long long
#define F first
#define S second
#define pii pair<int,int>
#define mpr make_pair
typedef long long ll;
const int maxn = 2e5+10;
const int mod = 1e9+7;
const ll inf = 1e18+10;
int n, m, k, t, a, b;
vector<int> g[maxn], H[maxn];
bool mark[maxn];
int dis[maxn];
vector<int> ve;
void bfs()
{
queue<int> q;
q.push(a); q.push(b);
dis[b] = dis[a] = 0;
mark[b] = mark[a] = 1;
while(q.size())
{
int v = q.front();
q.pop();
ve.push_back(v);
for(auto u : g[v])
if(!mark[u])
{
mark[u] = 1;
dis[u] = dis[v] + 1;
q.push(u);
}
}
}
bool isa[maxn], isb[maxn];
void dfs(int v, char tp)
{
if(tp == 'a') isa[v] = 1;
if(tp == 'b') isb[v] = 1;
mark[v] = 1;
for(auto u : H[v])
if(!mark[u]) dfs(u,tp);
}
int mn[maxn];
signed main()
{
ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);
cin>> n >> m >> k >> t >> a >> b;
for(int i = 1, u, v; i <= m; i++)
{
cin>> u >> v;
g[u].push_back(v);
g[v].push_back(u);
}
bfs();
for(int v = 1; v <= n; v++)
for(auto u : g[v])
if(dis[u] == dis[v]+1)
H[v].push_back(u);
memset(mark, 0, sizeof mark); dfs(a,'a');
memset(mark, 0, sizeof mark); dfs(b,'b');
for(int v = 1; v <= n; v++)
if(isa[v] && isb[v]) mn[v] = dis[v];
else mn[v] = inf;
for(auto v : ve)
for(auto u : H[v])
mn[u] = min(mn[u],mn[v]);
if(dis[t] < dis[k]) return cout<< -1, 0;
if(mn[t] == inf && mn[k] == inf)
{
if((isa[t] && isa[k]) || (isb[t] && isb[k])) cout<< dis[t] - dis[k];
else cout<< dis[t] - dis[k] - 1;
}
else
{
if(mn[t] < mn[k]) cout<< dis[t] - dis[k] - 1;
else cout<< dis[t] - dis[k];
}
}
