#include <bits/stdc++.h>
using namespace std;

#define SZ(a) (int)a.size()
#define ALL(a) a.begin(), a.end()
#define FOR(i, a, b) for (int i = (a); i<(b); ++i)
#define RFOR(i, b, a) for (int i = (b)-1; i>=(a); --i)
#define MP make_pair
#define PB push_back
#define F first
#define S second

typedef long long LL;
typedef pair<int, int> PII;
typedef vector<int> VI;

const int N = 1 << 17;

vector<int> g[N];
bool used[N];
int d[N];

int main()
{
	ios::sync_with_stdio(false);
	cin.tie(0);
	int n, m;
	cin >> n >> m;
	FOR(i, 0, n) {
		int x, y;
		cin >> x >> y;
	}
	while (m--) {
		int u, v;
		cin >> u >> v;
		u--;
		v--;
		g[u].push_back(v);
		g[v].push_back(u);
	}
	vector<int> vertices(n);
	iota(ALL(vertices), 0);
	sort(ALL(vertices), [](int u, int v) {return SZ(g[u]) > SZ(g[v]);});
	int ans = 5;
	for (int u : vertices) {
		used[u] = true;
		for (int v : g[u]) {
			if (!used[v]) {
				d[v] = 1;
			}
		}
		for (int v : g[u]) {
			if (used[v]) {
				continue;
			}
			for (int w : g[v]) {
				if (d[w] == 1) {
					ans = 3;
				}
				else if (d[w] == 2) {
					ans = min(ans, 4);
				}
				else {
					d[w] = 2;
				}
			}
		}
		for (int v : g[u]) {
			if (!used[v]) {
				for (int w : g[v]) {
					d[w] = 0;
				}
				d[v] = 0;
			}
		}
	}
	cout << ans << "\n";
	return 0;
}