#include<bits/stdc++.h>
#define rep(i,n) for(int i=0;i<(int)n;i++)
#define all(c) (c).begin(),(c).end()
#define pb push_back
#define dbg(...) do{cerr<<__LINE__<<": ";dbgprint(#__VA_ARGS__, __VA_ARGS__);}while(0);

using namespace std;

namespace std{template<class S,class T>struct hash<pair<S,T>>{size_t operator()(const pair<S,T>&p)const{return ((size_t)1e9+7)*hash<S>()(p.first)+hash<T>()(p.second);}};template<class T>struct hash<vector<T>>{size_t operator()(const vector<T> &v)const{size_t h=0;for(auto i : v)h=h*((size_t)1e9+7)+hash<T>()(i)+1;return h;}};}
template<class T>ostream& operator<<(ostream &os, const vector<T> &v){os<<"[ ";rep(i,v.size())os<<v[i]<<(i==v.size()-1?" ]":", ");return os;}template<class T>ostream& operator<<(ostream &os,const set<T> &v){os<<"{ "; for(const auto &i:v)os<<i<<", ";return os<<"}";}
template<class T,class U>ostream& operator<<(ostream &os,const map<T,U> &v){os<<"{";for(const auto &i:v)os<<" "<<i.first<<": "<<i.second<<",";return os<<"}";}template<class T,class U>ostream& operator<<(ostream &os,const pair<T,U> &p){return os<<"("<<p.first<<", "<<p.second<<")";}
void dbgprint(const string &fmt){cerr<<endl;}template<class H,class... T>void dbgprint(const string &fmt,const H &h,const T&... r){cerr<<fmt.substr(0,fmt.find(","))<<"= "<<h<<" ";dbgprint(fmt.substr(fmt.find(",")+1),r...);}
typedef long long ll;typedef vector<int> vi;typedef pair<int,int> pi;
const double EPS = 1e-8, INF = 1e12, PI = acos(-1.0);
typedef complex<double> P;
namespace std{
	bool operator<(const P& a, const P& b){
		return real(a) != real(b) ? real(a) < real(b) : imag(a) < imag(b);
	}
}
inline double cross(const P& a, const P& b){ return imag(conj(a)*b); }
inline double dot(const P& a, const P& b){ return real(conj(a)*b); }
struct L : public vector<P>{
	L(const P &a, const P &b) {
		push_back(a); push_back(b);
	}
};
typedef vector<P> G;
inline int ccw(P a, P b, P c) {
	b -= a; c -= a;
	if(cross(b, c) >  EPS)   return +1;      // counter clockwise
	if(cross(b, c) < -EPS)   return -1;      // clockwise
	if(dot(b, c)   < -EPS)   return +2;      // c--a--b on line
	if(norm(b)+EPS <norm(c)) return -2;      // a--b--c on line
	return 0;                                   // c is between a and b (inclusive)
}
#define curr(P, i) P[i]
#define next(P, i) P[(i+1)%P.size()]
double area2(const G& g) {
	double A = 0;
	for (int i = 0; i < g.size(); ++i) 
		A += cross(curr(g, i), next(g, i));
	return A;
}

int main(){
	cin.tie(0); cin.sync_with_stdio(0);
	int c, w;
	while(cin >> c >> w, c){
		G vs;
		vector<vi> v_to_es(c);
		rep(i, c){ int x, y; cin >> x >> y; vs.emplace_back(x, y); }
		rep(i, w){
			int s, t; cin >> s >> t; s--; t--;
			v_to_es[s].pb(t);
			v_to_es[t].pb(s);
		}
		rep(i, c){
			sort(all(v_to_es[i]), [&](int a, int b){
				return arg(vs[a] - vs[i]) < arg(vs[b] - vs[i]);
			});
		}
		
		int outer = -1;
		vector<vi> sur;
		set<pi> vis;
		map<pi,int> e_to_sur;
		
		function<void(int,int,vi&)> rec = [&](int prev, int cur, vi &v){
			vis.emplace(prev, cur);
			v.pb(prev);
			int k = 0;
			for(; v_to_es[cur][k] != prev; k++);
			k = (k - 1 + v_to_es[cur].size()) % v_to_es[cur].size();
			int next = v_to_es[cur][k];
			if(!vis.count(pi(cur, next))) rec(cur, next, v);
		};
		rep(i, c) for(int j : v_to_es[i]) if(!vis.count(pi(i, j))){
			vi v;
			rec(i, j, v);
			int id = sur.size();
			G g;
			rep(k, v.size()){
				e_to_sur[pi(v[k], v[(k+1) % v.size()])] = id;
				g.pb(vs[v[k]]);
			}
			if(area2(g) < 0) outer = id;
			sur.pb(v);
			//dbg(v, area2(g));
		}
		
		//dbg(outer);
		int n = sur.size();
		vector<vi> dist(n, vi(n, 10000));
		rep(i, n) dist[i][i] = 0;
		rep(i, n) rep(j, sur[i].size()){
			int k = e_to_sur[pi(sur[i][(j + 1) % sur[i].size()], sur[i][j])];
			dist[i][k] = dist[k][i] = 1;
		}
		rep(k, n) rep(i, n) rep(j, n) dist[i][j] = min(dist[i][j], dist[i][k] + dist[k][j]);
		cout << *max_element(all(dist[outer])) << endl;
	}
	return 0;
}


Measured memory_bytes: 3480