#include <iostream>
#include <cmath>
#include <vector>
#include <queue>
using namespace std;
typedef long long ll;
const int maxn = 1e5 + 10;
vector<int> graph[maxn];
int n, m;
int bfs(int S, int E) {
    queue<int> q;
    q.push(S); // current node
    q.push(0); // shortest distance from starting node to current node
    vector<bool> visited(n + 1, false);
    visited[S] = true;
    while(!q.empty()) {
        int current_node = q.front(); q.pop();
        int shortest_distance_from_start_till_now = q.front(); q.pop();
        if(current_node == E) {
            return shortest_distance_from_start_till_now;
        }
        for(int i = 0; i < (int) graph[current_node].size(); ++i) {
            int neighbour = graph[current_node][i];
            if(!visited[neighbour]) {
                visited[neighbour] = true;
                q.push(neighbour);
                q.push(shortest_distance_from_start_till_now + 1);
            }
        }
    }
    return -1;
}
int main()
{
    ios_base::sync_with_stdio(false);
    cin >> n >> m;
    for(int i = 0; i < m; ++i) {
        int a, b;
        cin >> a >> b;
        graph[a].push_back(b);
        graph[b].push_back(a);
        //undirected graph
    }
    int start, end;
    cin >> start >> end;
    cout << bfs(start, end) << endl;
    return 0;
}