propram Tinh_tich;

uses crt;

var T,n,i:integer;

begin

clrscr;

write('Nhap so n'); readln(n);

while n mod 2 =0 do

begin

readln(n);

end;

P:=2;

for i:=2 to n do

if i mod 2 <>0 then P:=P*i;

write('Tich la:',P);

end.

`@`Dùng For..do:

Program baitap;
Uses crt;
Var n,i:integer;
    P:extended;
Begin
Clrscr;
Write('n='); Readln(n);
P:=1;
For i:=1 to n do
     If i mod 2=0 then P:=P*i;
Writeln('P=',trunc(P));
Readln
End.

`@`Dùng While..do:

Program baitap;
Uses crt;
Var n,i:integer;
    P:extended;
Begin
Clrscr;
Write('n='); Readln(n);
P:=1;i:=1;
While i<=n do
     Begin
     If i mod 2=0 then P:=P*i;
     inc(i);
     End;
Writeln('P=',trunc(P));
Readln
End.

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Đã test code