Interschimbare elemente

>Se citesc de la tastatura 4 numere reale: a,b,c,d. Sa se interschimbe circular de la stinga la dreapta valorile lor. De exemplu pentru a=10,b=20,c=30,d=40 dupa interschimbare obtinem a=40,b=10,c=20,d=30.

 program p1;
 uses crt;
 var m,a,b,c,d:real;
 begin
 clrscr;
 write('A='); readln(a);
 write('b='); readln(b);
 write('c='); readln(c);
 write('d='); readln(d);
 m:=d;
 d:=c;
 c:=b;
 b:=a;
 a:=m;
 write('dupa schimbare');
 writeln('A=',a:2:0);
 writeln('b=',b:2:0);
 writeln('c=',c:2:0);
 writeln('d=',d:2:0);
 readkey;
 end.
{by viktoritza}