stack1.pas

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program E1_2; {stack_count1}
var count:longint;
    n,i,top,head:integer;
    a:array[1..100] of byte;
    input,output:text;

procedure init;
begin
 assign(input,'stack1.in'); reset(input);
 readln(input,n); close(input);
 for i:=1 to n do a[i]:=0;
 head:=1; top:=0
end;

procedure push;
begin   inc(top);  a[top]:=head;  inc(head) end;

procedure pop;
begin a[top]:=0; dec(top)  end;

procedure work;
var j,k:byte;
begin
 if (top=0) and (head=n+1)  then  inc(count)
  else
   for j:=1 to 2 do
    begin
     if (j=2) and (top>0) then
      begin
          k:=a[top];
          pop;
          work;
          inc(top);
          a[top]:=k;
      end;
     if (j=1) and (head<n+1) then
      begin
        push;
        work;
        dec(top);
        dec(head);
      end;
    end
end;
procedure print;
begin
 assign(output,'stack1.out'); rewrite(output);
 writeln(output,count); close(output)
end;

begin
 init; work; print
end.