#pragma comment(linker, "/STACK:102400000, 102400000")

#include<cstdio>

#include<cstring>

#include<cstdlib>

#include<cctype>

#include<cmath>

#include<iostream>

#include<sstream>

#include<iterator>

#include<algorithm>

#include<string>

#include<vector>

#include<set>

#include<map>

#include<stack>

#include<deque>

#include<queue>

#include<list>

#define Min(a, b) ((a < b) ? a : b)

#define Max(a, b) ((a < b) ? b : a)

const double eps = 1e-8;

inline int dcmp(double a, double b) {

    if(fabs(a - b) < eps)  return 0;

    return a < b ? -1 : 1;

}

typedef long long LL;

typedef unsigned long long ULL;

const int INT_INF = 0x3f3f3f3f;

const int INT_M_INF = 0x7f7f7f7f;

const LL LL_INF = 0x3f3f3f3f3f3f3f3f;

const LL LL_M_INF = 0x7f7f7f7f7f7f7f7f;

const int dr[] = {0, 0, -1, 1, -1, -1, 1, 1};

const int dc[] = {-1, 1, 0, 0, -1, 1, -1, 1};

const int MOD = 1e9 + 7;

const double pi = acos(-1.0);

const int MAXN = 1000 + 10;

const int MAXT = 10000 + 10;

using namespace std;

struct Point{

    double x, y;

    void set(double xx, double yy){

        x = xx;

        y = yy;

    }

};

double getArea(Point &A, Point &B){

    return A.x * B.y - A.y * B.x;

}

int main(){

    int N;

    while(scanf("%d", &N) == 1){

        if(!N) return 0;

        Point A, B;

        scanf("%lf%lf%lf%lf", &A.x, &A.y, &B.x, &B.y);

        double L = 0;

        double area = 0;

        for(int i = 0; i < N; ++i){

            double l;

            scanf("%lf", &l);

            L += l;

            area += l * l / 2;

        }

        double k1 = A.y / A.x;

        double k2 = B.y / B.x;

        if(k1 > k2){

            swap(k1, k2);

        }

        double x1 = (k2 + 1) * L / (k2 - k1);

        double y1 = k1 * x1;

        double x2 = (k1 + 1) * L / (k2 - k1);

        double y2 = k2 * x2;

        A.set(x1, y1);

        B.set(x2, y2);

        double ans = getArea(A, B) / 2 - area;

        printf("%.3lf\n", ans);

    }

    return 0;

}