#include <iostream>

#include <vector>

#include <list>

using namespace std;

int N;

int A, B;

vector<int> relatives[100];

int b[100];

bool visited[100];

list<int> bfsQueue;

int ans = -1;

void bfs() {

if (bfsQueue.empty()) return;

int x = bfsQueue.front(); bfsQueue.pop_front();

for (int r : relatives[x]) {

if (!visited[r]) {

visited[r] = true;

if (r == B - 1) {

ans = b[x] + 1;

return;

}

else {

b[r] = b[x] + 1;

bfsQueue.push_back(r);

}

}

}

bfs();

}

int main()

{

cin >> N >> A >> B;

int i, n, x, y;

cin >> n;

for (i = 0; i < n; i++) {

cin >> x >> y;

relatives[x - 1].push_back(y - 1);

relatives[y - 1].push_back(x - 1);

}

bfsQueue.push_back(A-1);

visited[A - 1] = true;

bfs();

cout << ans;

}