#include <iostream>#include <cstring>#include <cstdlib>#include <cstdio>#include <queue>#include <cmath>#include <algorithm>#define LL long long#define EPS (1e-8)const double Double_PI = 2.0*acos(-1.0);using namespace std;struct P{ double x,y;}sp[100100],p[100100];int top;bool cmp(P p1,P p2){ if(fabs(p1.x - p2.x) < EPS) { return p1.y < p2.y; } return p1.x < p2.x;}double X_Mul(P a1,P a2,P b1,P b2){ P v1 = {a2.x-a1.x , a2.y-a1.y},v2 = {b2.x-b1.x , b2.y-b1.y}; return (v1.x*v2.y-v1.y*v2.x);}P Line_Cross_Position(P l1,P l2,P s1,P s2){ P cp = s1; double t = fabs(X_Mul(l1,l2,l1,s1)) / fabs(X_Mul(l1,l2,s2,s1)); cp.x += t*(s2.x-s1.x); cp.y += t*(s2.y-s1.y); return cp;}double Cal_Angle(P a1,P a2,P b1,P b2){ P v1 = {a2.x-a1.x,a2.y-a1.y},v2 = {b2.x-b1.x,b2.y-b1.y}; if(fabs(X_Mul(a1,a2,b1,b2)) < EPS) return 0; if(X_Mul(a1,a2,b1,b2) >= EPS) return acos((v1.x*v2.x+v1.y*v2.y)/(sqrt( (v1.x*v1.x + v1.y*v1.y)*(v2.x*v2.x + v2.y*v2.y) ))); return -acos((v1.x*v2.x+v1.y*v2.y)/(sqrt( (v1.x*v1.x + v1.y*v1.y)*(v2.x*v2.x + v2.y*v2.y) ) ) );}double Cal_Point_Dis(P p1,P p2){ return sqrt( (p1.x-p2.x)*(p1.x-p2.x) + (p1.y-p2.y)*(p1.y-p2.y) );}double Point_In_Segment(P p,P p1,P p2){ if( fabs(Cal_Point_Dis(p1,p2) - Cal_Point_Dis(p,p1) - Cal_Point_Dis(p,p2) ) < EPS) return true; return false;}bool Is_Point_In_Polygon(P tp,int n){ int i; double asum = 0; for(i = 0;i < n; ++i) { asum += Cal_Angle(tp,p[i],tp,p[i+1]); } if(fabs(fabs(asum) - Double_PI) < EPS) return true; for(i = 0;i < n; ++i) { if(Point_In_Segment(tp,p[i],p[i+1]) ) return true; } return false;}double Length_In_Polygon(P pa,P pb,int n){ double lsum,xm1,xm2; int i; P temp; for(i = 0;i < n; ++i) { xm1 = X_Mul(pa,pb,pa,p[i]); xm2 = X_Mul(pa,pb,pa,p[i+1]); if(xm1*xm2 < -EPS) { sp[top++] = Line_Cross_Position(pa,pb,p[i],p[i+1]); } else { if(fabs(xm1) < EPS) sp[top++] = p[i]; if(fabs(xm2) < EPS) sp[top++] = p[i+1]; } } sort(sp,sp+top,cmp); for(i = 1,lsum = 0;i < top; ++i) { temp.x = (sp[i].x + sp[i-1].x)/2; temp.y = (sp[i].y + sp[i-1].y)/2; if(Is_Point_In_Polygon(temp,n)) { lsum += Cal_Point_Dis(sp[i],sp[i-1]); } } return lsum;}int main(){ int i,n,m; P pa,pb; while( scanf("%d %d",&n,&m) && (n||m) ) { for(i = 0;i < n; ++i) { scanf("%lf %lf",&p[i].x,&p[i].y); } p[n] = p[0]; while(m--) { scanf("%lf %lf %lf %lf",&pa.x,&pa.y,&pb.x,&pb.y); top = 0; printf("%.3lfn",Length_In_Polygon(pa,pb,n)); } } return 0;}
