URAL 1966

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<iostream>
#include<cmath>
using namespace std;

const double eps = 1e-8;

int dcmp(double d) {
return d < -eps ? -1 : d > eps;
}

struct Point {
double x, y;
Point() {}
Point(double x, double y)
: x(x), y(y) {}

Point operator + (const Point& a) const {
return Point(x + a.x, y + a.y);
}
Point operator - (const Point& a) const {
return Point(x - a.x, y - a.y);
}
Point operator * (double k) const {
return Point(x * k, y * k);
}
Point operator / (double k) const {
return Point(x / k, y / k);
}
double cross(const Point& a) const {
return (x * a.y - y * a.x);
}
double dot(const Point& a) const {
return x * a.x + y * a.y;
}
void read() {
scanf("%lf%lf", &x, &y);
}
bool operator < (const Point& a) const {
return x < a.x || (x == a.x && y < a.y);
}
bool operator == (const Point& a) const {
return dcmp(x - a.x) == 0 && dcmp(y - a.y) == 0;
}
double length() {
return sqrt(x * x + y * y);
}
};
struct Line {
Point a, b;

Line() {}
Line(const Point& a, const Point& b)
:a(a), b(b) {}

bool onSegment(Point p) {// 判断点是否在线段上
return dcmp((p - a).cross(b - a)) == 0 && dcmp((a - p).dot(b - p)) <= 0;
}
int segCrossSeg(const Line &u) {// 判断线段是否相交
int d1 = dcmp((b - u.a).cross(a - u.a));
int d2 = dcmp((b - u.b).cross(a - u.b));
int d3 = dcmp((u.b - a).cross(u.a - a));
int d4 = dcmp((u.b - b).cross(u.a - b));
if ((d1 ^ d2) == -2 && (d3 ^ d4) == -2) return 2;
return ((d1 == 0 && dcmp((b - u.a).dot(a - u.a)) <= 0)
|| (d2 == 0 && dcmp((b - u.b).dot(a - u.b)) <= 0)
|| (d3 == 0 && dcmp((u.b - a).dot(u.a - a)) <= 0)
|| (d4 == 0 && dcmp((u.b - b).dot(u.a - b)) <= 0));
}
};
//************************模板********************************************//
Point p[250];
int fa[250];
int eu[250],ev[250];
int n,m;
int getFather(int x){
if(fa[x]==-1)
return x;
return fa[x]=getFather(fa[x]);
}
int main() {

while(cin>>n>>m)
{
memset(fa,-1,sizeof(fa));
for(int i=1;i<=n;i++)
p[i].read();
for(int i=1;i<=m;i++)
{
cin>>eu[i]>>ev[i];
int fu=getFather(eu[i]);
int fv=getFather(ev[i]);
if(fu!=fv)
fa[fu]=fv;
}
for(int i=1;i<=m;i++)
{
Line l(p[eu[i]],p[ev[i]]);
for(int j=1;j<=n;j++)
{
if(l.onSegment(p[j])==0)continue;
int fu=getFather(j);
int fv=getFather(eu[i]);
if(fu!=fv)
fa[fu]=fv;
}
}
for(int i=1;i<=m;i++)
for(int j=i+1;j<=m;j++)
{
Line l1(p[eu[i]],p[ev[i]]);
Line l2(p[eu[j]],p[ev[j]]);
if(l1.segCrossSeg(l2)==0)continue;
int fu=getFather(eu[j]);
int fv=getFather(eu[i]);
if(fu!=fv)
fa[fu]=fv;
}
int cnt=0;
for(int i=1;i<=n;i++)
if(fa[i]==-1)
cnt++;
if (cnt == 1) puts("YES");
else puts("NO");
}
return 0;
}