//#define _GLIBCXX_DEBUG
#define _CRT_SECURE_NO_WARNINGS
#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef long double ld;

#define mk make_pair
#define inb push_back
#define X first
#define Y second
#define all(v) v.begin(), v.end()
#define sqr(x) (x) * (x)
#define TIME 1.0 * clock() / CLOCKS_PER_SEC
#define y1 AYDARBOG
//continue break pop_back return scanf

int solve();

int main()
{
    //ios_base::sync_with_stdio(0);
    //cin.tie(0);
#define TASK ""
#ifndef _DEBUG
    //freopen(TASK".in", "r", stdin), freopen(TASK".out", "w", stdout);
#endif
    solve();
#ifdef _DEBUG
    fprintf(stderr, "\nTIME: %.3f\n", TIME);
#endif
}

const int BUFSZ = (int)1e5 + 7;
char buf[BUFSZ];
string get_str()
{
    scanf(" %s", buf);
    return string(buf);
}

const int M = 1e5 + 5;

int n, m, s, f, k, VAL;
vector<int> g[M];
int was[M], us[M];

int bfs()
{
    queue<int> q;
    us[s] = 1;
    q.push(s);
    while(q.size())
    {
        int v = q.front();
        q.pop();
        for(auto to : g[v])
            if (!us[to])
            {
                us[to] = us[v] + 1;
                q.push(to);
            }
    }
    return us[f];
}

bool dfs(int x)
{
    queue<int> q;
    q.push(k);
    for(int i = 1; i <= n; ++i) was[i] = 0;
    was[k] = 1;
    while(q.size())
    {
        int v = q.front();
        q.pop();
        for(auto to : g[v])
            if (!was[to] && was[v] + 1 <= x + 1)
            {
                was[to] = was[v] + 1;
                q.push(to);
            }
    }
    for(int i = 1; i <= n; ++i) us[i] = 0;
    if (!was[s]) us[s] = 1, q.push(s);
    while(q.size())
    {
        int v = q.front();
        q.pop();
        for(auto to : g[v])
            if (!us[to] && !was[to])
            {
                us[to] = us[v] + 1;
                q.push(to);
            }
    }
    return (us[f] != VAL);
}

int solve()
{
    scanf("%d%d", &n, &m);
    for(int i = 0, a, b; i < m; ++i)
    {
        scanf("%d%d", &a, &b);
        g[a].inb(b);
        g[b].inb(a);
    }
    scanf("%d%d%d", &s, &f, &k);
    VAL = bfs();
    int l = 0, r = n;
    while(l < r)
    {
        int mid = (l + r) >> 1;
        if (dfs(mid)) r = mid;
        else l = mid + 1;
    }
    printf("%d\n", l);
    return 0;
}