Program BTH; uses crt; var n,i:longint; s:word; begin clrscr;
Repeat write('Nhap n: ');readln(n); If n mod 2=1 then writeln('So nhap khong hop le moi nhap lai'); until n>0; s:=1; For i:=1 to n do s:=s*i; write('Tong day so tren la: ',s); readln; end.