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//#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);
//}
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