#include <vector>#include <list>#include <map>#include <set>#include <deque>#include <stack>#include <bitset>#include <algorithm>#include <functional>#include <numeric>#include <utility>#include <sstream>#include <iostream>#include <iomanip>#include <cstdio>#include <cmath>#include <cstdlib>#include <ctime>#include <cstring>#include<iostream>#include<cstring>using namespace std;const double PI = acos(-1.0);#define EPS 1e-7double f(double a,double b,double l){ l=l*l; double ret; // printf("%lf %lf %lfn",a,b,l); ret=l*sin(a+b+PI/4)*sin(a+PI/4)/sin(b); return ret;}int main(){ int n; double xa,ya,xb,yb; while (scanf("%d", &n) == 1) { if(!n) break; double len[11]; scanf("%lf%lf%lf%lf",&xa,&ya,&xb,&yb); double ang1=atan2(ya,xa),ang2=atan2(yb,xb); if(ang1>ang2) swap(ang1,ang2); ang2=ang2-ang1; double tot=0; for(int i=0;i<n;i++) { scanf("%lf",&len[i]); tot+=len[i]; } if(fabs(ang2)<EPS) puts("0.000"); else { double ans=f(ang1,ang2,tot); for(int i=0;i<n;i++) ans-=len[i]*len[i]/2; printf("%.3lfn",ans+EPS); } } return 0;}
