How to enter a variable in an INPUT ?

[What_Else]

Hello, I bought an HP Prime there is very little time!
I wanted to test the HP Prime Basic language by doing a vector product calculation program.
The problem is that I can not at all include variables in INPUT (I wish I could enter 4x for example instead of 4)
Code:

EXPORT Produit_Vectoriel()
BEGIN

LOCAL A,B,C,D,E,F;
LOCAL X,Y,Z,N;

INPUT({A,B,C},"Vecteur 1",{"X = ","Y = ","Z = "});

INPUT({D,E,F},"Vecteur 2",{"X' = ","Y' = ","Z' = "});
CAS("B*F*-C*E▶X");
C*D-A*F▶Y;
A*E-B*D▶Z;
CAS("sqrt(X^2+Y^2+Z^2)▶N");


PRINT();
PRINT(" ");
PRINT(" Résultat :");
PRINT(" |"+X);
PRINT(" |"+Y);
PRINT(" |"+Z);
PRINT(" ");
PRINT(" Norme : "+N);

END;

Thank you