format long;
a=-0.2488;
b=-0.0493;
c=0.1321;
d=0.2988;
x1=a-b;
x2=a-c;
x3=a-d;
x4=b-c;
x5=b-d;
x6=c-d;
x=-(b*c*d*0.3/x1/x2/x3-a*c*d*0.4/x4/x5/x1+a*b*d*0.5/x2/x4/x6-a*b*c*0.6/x3/x5/x6)