#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;
}