#include <bits/stdc++.h>
using namespace std;
vector<int> gr[10000];
queue<int> q;
int n,m;
int BFS(int a, int b)
{
    int d[n]={-1};
    d[a]=1;
    q.push(a);int ras=-1;

    while(!q.empty())
        {
            ras=q.front();
    q.pop();
    }
    for(int s: gr[ras])
    {
        if (d[s]==-1)
        {
            q.push(s);d[a]=d[ras]+1;
        }

    }
    return d[b];
}
int main()
{
    cin>>n>>m;
    for(int i=0;i<m;i++){
        int v,v2;
        cin>>v>>v2;
        gr[v].push_back(v2);
         gr[v2].push_back(v);
    }
    int a,b;
    cin>>a>>b;
    cout<<BFS(a,b);
}