#include<bits/stdc++.h>
using namespace std;
int n,m,ans;
int a,b;
bool flag[1005];
int vis[1005];
vector<vector<int>> maap;
void dfs(int x){
    if(x == b){ //到达了终点
        ans++;//可走的路径＋1
        for(int i = 0;i < n;i++){
            if(flag[i] == true){
                vis[i]++;
            }
        }
        return;
    }
    for(int i = 0;i < maap[x].size();i++){
        if(flag[maap[x][i]] == false){
            flag[maap[x][i]] = true;
            dfs(maap[x][i]);
            flag[maap[x][i]] = false;
        }
    }
}
int main() {
    cin>>n>>m;
    maap.resize(n+2);
    memset(vis, 0, sizeof(vis));
    for(int i = 0;i < m;i++){
        int x,y;
        cin >> x >> y;
        maap[x].push_back(y);
        maap[y].push_back(x);
    }
    
    cin >> a >> b;
    dfs(a);
    if(ans == 0){
        cout << "-1" << endl;
        return 0;
    }
    int res = 0;
    for(int i = 0;i < n;i++){
        if(vis[i] == ans){
            res++;
        }
    }
    cout << res-1 << endl;
    return 0;
}