Program Acm_Timus_Ru_1298;
const dy:array [1..8] of integer=(-2,-2,-1,1,2,2,1,-1);
      dx:array [1..8] of integer=(-1,1,2,2,1,-1,-2,-2);
      g:array [1..8] of char=('a','b','c','d','e','f','g','h');

      var a:array [-5..15,-5..15] of longint;
          k,i,j,ip,min,h,x,y,rem:longint;
          n                     : longint;
          p                     : boolean;


Function mo(x,y:integer):boolean;
Begin
   if (x>n) or (x<1) or (y>n) or (y<1) then mo:=false
                                       else mo:=a[x,y]=0;
End;

Function hm(x,y:integer):byte;
Var i:integer;
Begin
   k:=0;
   if not(mo(x,y)) then k:=n*n
                   else for i:=1 to 8 do
                             if mo(x+dx[i],y+dy[i]) then k:=k+1;
   hm:=k;
End;

BEGIN
  readln(n);
  if (n>=1) and (n<=8) then
  begin
     fillchar(a,sizeof(a),0);
     x:=1;y:=1;
     for i:=1 to n*n do
     begin
      min:=n*n;
      a[x,y]:=i;
      for j:=1 to 8 do
       begin
         h:=hm(x+dx[j],y+dy[j]);
         if h<min then
           begin
             ip:=j;
             min:=h;
           end;
       end;
        x:=x+dx[ip];
        y:=y+dy[ip];
    end;
 p:=true;
 for i:=1 to n do
 for j:=1 to n do
 if a[i,j]=0 then p:=false;
 if p=false then begin writeln('IMPOSSIBLE');end
            else
              for k:=1 to n*n do
              for i:=1 to n do
              for j:=1 to n do
                if a[i,j]=k then writeln(g[i],j);
  end
  else
    writeln('IMPOSSIBLE');
END.

I think the problem is here-

x:=x+dx[ip];
y:=y+dy[ip];

may be ip is invalid since it might not be updated. When all the neighbor squares return hm()>=min value, ip will not get updated.

It's very intresting!
I compiled given source code both on
Delphi and FreePascal and checked each
program on every possible tests (n from 1 to 8)
and I didn't get Access Violation.
I am really confused if this code get Access Violation
on Timus Judge System.

It's very interesting, I wrote a new program in which answers for 5,6,7,8 were constants (which I defined by my program which gets Crash on a server), and I got AC.

Admins!
Can you give some clarification to this situation?
Is it a crash of the program or a Judge?

Add ip:=7862341 line after BEGIN, and you'll get crash in both Delphi and FreePascal.

I know that ip was not initialized.
Delphi gave that warning, but why
does the same program run different on
my home machine and on timus server.

I have no crashes on all possible tests.

How do you compile sources exactly?

If variable is not initialized it may have arbitrary value, that depends on many factors. It must work different on different machines!