//By SiriusRen#include <bits/stdc++.h>#define double long doubleusing namespace std;const int N=100050;const double eps=1e-10;int n,m,xx,yy,tot;double Ans;vector<int>vec[N];struct Point{double x,y;}point[N];struct Line{Point a,b;double angle;}line[N],q[N];void addline(Line &l,Point a,Point b){    l.a=a,l.b=b,l.angle=atan2(b.y-a.y,b.x-a.x);}Point operator-(Point a,Point b){    Point c;c.x=a.x-b.x,c.y=a.y-b.y;return c;}double operator*(Point a,Point b){    return a.x*b.y-a.y*b.x;}bool operator<(Line a,Line b){    if(a.angle==b.angle)return (b.b-a.a)*(b.a-a.a)>0;    return a.angle<b.angle;}Point inter(Line a,Line b){    double k1,k2,t;    k1=(a.b-b.a)*(b.b-b.a);    k2=(b.b-b.a)*(a.a-b.a);    t=k1/(k1+k2);    Point ans;    ans.x=a.b.x+(a.a.x-a.b.x)*t;    ans.y=a.b.y+(a.a.y-a.b.y)*t;    return ans;}double dis(Point x,Point y){    x=y-x;    return sqrt(x.x*x.x+x.y*x.y);}bool judge(Line a,Line b,Line t){    Point p=inter(a,b);    return (t.a-p)*(t.b-p)<0;}void bpmj(){    sort(line+1,line+1+tot);    n=0;    for(int i=1;i<=tot;i++){        if(abs(line[i].angle-line[i-1].angle)>eps)n++;        line[n]=line[i];    }    int r=1,l=0;    q[0]=line[1],q[1]=line[2];    for(int i=3;i<=n;i++){        while(l<r&&judge(q[r],q[r-1],line[i]))r--;        while(l<r&&judge(q[l],q[l+1],line[i]))l++;        q[++r]=line[i];    }    while(l<r&&judge(q[r],q[r-1],q[l]))r--;    while(l<r&&judge(q[l],q[l+1],q[r]))l++;    q[r+1]=q[l],tot=0;    for(int i=l;i<=r;i++)point[++tot]=inter(q[i],q[i+1]);    point[++tot]=point[1];    for(int i=1;i<tot;i++)Ans+=dis(point[i],point[i+1]);}int main(){    scanf("%d%d",&n,&m);    for(int i=1;i<=n;i++)        scanf("%Lf%Lf",&point[i].x,&point[i].y);    Ans=-dis(point[1],point[n]);    for(int i=1;i<=m;i++){        scanf("%d%d",&xx,&yy);        if(xx>yy)swap(xx,yy);        vec[xx].push_back(yy);    }    for(int i=1,j,k;i<=n;i++){        sort(vec[i].begin(),vec[i].end());        for(j=n,k=vec[i].size()-1;j>i&&~k;j--,k--)            if(vec[i][k]!=j)break;        if(i==1&&j==n){printf("%.10Lf\n",dis(point[1],point[n]));return 0;}        if(j>i)addline(line[++tot],point[j],point[i]);    }addline(line[++tot],point[1],point[n]);    bpmj();    printf("%.10Lf\n",Ans);}