//#include <gtest/gtest.h>

#include <iostream>
#include <vector>
#include <queue>

using std::vector;
using std::queue;

void bfs(vector<vector<int>> &adj, int s, vector<int> &dist) {
	queue<int> vertexQ;
	vertexQ.push(s);

	while (!vertexQ.empty()) {
		int u = vertexQ.front();
		vertexQ.pop();
		for (int i : adj[u]) {
			if (dist[i] == -1) {
				vertexQ.push(i);
				dist[i] = dist[u] + 1;
			}
		}
	}
}

int distance(vector<vector<int> > &adj, int s, int t) {
	vector<int> dist(adj.size(), -1);
	dist[s] = 0;

	bfs(adj, s, dist);

	return dist[t];
}

int main() {
	int n, m;
	std::cin >> n >> m;
	vector<vector<int> > adj(n, vector<int>());
	for (int i = 0; i < m; i++) {
		int x, y;
		std::cin >> x >> y;
		adj[x - 1].push_back(y - 1);
		adj[y - 1].push_back(x - 1);
	}
	int s, t;
	std::cin >> s >> t;
	s--, t--;
	std::cout << distance(adj, s, t);
}

//TEST(Acyclicity, ac1) {
//	vector<vector<int>> adj = { { 1 }, { 2 }, { 0 }, { 0 } };
//	ASSERT_EQ(acyclic(adj), 1);
//}