I simply multiple N by 2 and then find Trunc(Sqrt(2*N)). Isn't that
correct? Why do I get WA?
Here is my program:


Program Sqrt;
 Const Max=1300;
 Var s:String;
     a,b,c,e:Array[1..Max] Of Byte;
     v,d,l,p,i,j,k,m,n:Longint;
     mr:Boolean;
Begin
 Readln(s);
 l:=Length(s);
 FillChar(a,SizeOf(a),0);
 For i:=1 To l Do
  a[i+1]:=Ord(s[i])-Ord('0');
 Inc(l);
 d:=0;
 For i:=l DownTo 1 Do Begin
  v:=a[i]*2+d;
  b[i]:=v Mod 10;
  d:=v Div 10;
 End;
 Move(b,a,SizeOf(a));
 If l Mod 2=1 Then
  If a[1]>0 Then Begin
   Inc(l);
   For i:=l DownTo 2 Do
    a[i]:=a[i-1];
  End Else Begin
   Dec(l);
   For i:=1 To l Do
    a[i]:=a[i+1];
  End;
 FillChar(b,SizeOf(b),0);
 p:=(l+1) Div 2;
 For i:=1 To p Do Begin
  For j:=1 To 9 Do Begin
   b[i]:=j;
   FillChar(c,SizeOf(c),0);
   For k:=i DownTo 1 Do Begin
    d:=0;
    For m:=i DownTo 1 Do Begin
     v:=b[k]*b[m]+d+c[k+m];
     c[k+m]:=v Mod 10;
     d:=v Div 10;
    End;
    If d>0 Then
     c[k]:=c[k]+d;
   End;
  mr:=False;
  For k:=1 To i*2 Do
   If a[k]<c[k] Then Begin
    mr:=True;
    Break;
   End Else If a[k]>c[k] Then
    Break;
  If mr Then Begin
   Dec(b[i]);
   Break;
  End;
  End;
 End;
 i:=1;
 While b[i]=0 Do
  Inc(i);
 For j:=i To p Do
  Write(b[j]);
 Writeln;
End.