#include <iostream>
#include<ctime>
#include<map>
#include<vector>
#include<queue>
#include <algorithm>
using namespace std;
int main()
{
    int n, m;
    cin >> n >> m;
    vector<int> graph[n + 5];
    bool visited[n + 5];
    for(int i = 0; i <= n; i++) {
        visited[i] = false;
    }
    for(int i = 0; i < m; i++) {
        int a, b;
        cin >> a >> b;
        graph[a].push_back(b);
        graph[b].push_back(a);
    }
    int S, T;
    cin >> S >> T;
    
    queue<int> q;
    q.push(S); // pocetno teme
    q.push(0); // distanca od S do S
    visited[S] = true;
    
    while(!q.empty()) {
        int teme = q.front();
        q.pop();
        int dist = q.front();
        q.pop();
        
        if(teme == T) {
            cout << dist << endl;
            return 0;
        }
        
        for(int i = 0; i < graph[teme].size(); i++) {
            int sosed = graph[teme][i];
            if(!visited[sosed]) {
                q.push(sosed);
                q.push(dist + 1);
                visited[sosed] = true;
            }
        }
        
    }
    cout << 0 << endl;
    return 0;
}