Тождество (разбор строк)

Var z,e:char; s:string; k1,k2,k3,l1,l2,l3,t,i:integer; s1,s2,s3:int64;
  begin
    readln(s); t:=1;
  
  if s[1]='-' then begin k1:=-1; l1:=l1+1; t:=2; end else k1:=1;
    for i:=t to length(s) do 
      if s[i] in ['0'..'9'] then begin s1:=s1*10+strtoint(s[i]); l1:=l1+1; end else begin t:=i; break; end;
   s1:=s1*k1;
   
   z:=s[t]; t:=t+1;
   
   if s[t]='-' then begin k2:=-1; l2:=l2+1; t:=t+1 end else k2:=1;
    for i:=t to length(s) do 
      if s[i] in ['0'..'9'] then begin s2:=s2*10+strtoint(s[i]); l2:=l2+1; end else begin t:=i; break; end;
        s2:=s2*k2;
    e:=s[t]; t:=t+1;
    
     if s[t]='-' then begin k3:=-1; l3:=l3+1; t:=t+1 end else k3:=1;
    for i:=t to length(s) do
      if s[i] in ['0'..'9'] then begin s3:=s3*10+strtoint(s[i]); l3:=l3+1; end else begin t:=i; break; end;
      s3:=s3*k3;
   if (l1+l2+l3+2<>length(s)) or (l1=0) or (l2=0) or (l3=0) or (e<>'=') or (not (z in ['+','-','/','*'])) then begin write('ERROR'); exit;end;
   
   case z of
     '+': begin if s1+s2=s3 then write('YES') else write('NO'); end;
     '-':begin if s1-s2=s3 then write('YES') else write('NO'); end;
     '*':begin if s1*s2=s3 then write('YES') else write('NO'); end;
     '/':begin if (s2<>0)and(s1 div s2=s3) then write('YES') else write('NO'); end;
   end;
  end.

## {$zerobasedstrings}
 
procedure Error;
begin
  Write('Error');
  Halt;
end;
function NextSym(s: string; var i: integer): char;
begin
  if i=s.Length then Error;
  Result := s[i];
  i += 1;
end;
 
function NextNum(s: string; var i: integer): integer;
begin
  var ch := NextSym(s,i);
  
  var k := 1;
  begin
    if ch='-' then
    begin
      k := -1;
      ch := NextSym(s,i);
    end;
    if ch in '0'..'9' then
      Result := ch.ToDigit else
      Error;
  end;
  
  var li := i;
  while true do
  begin
    if li=s.Length then break;
    ch := NextSym(s,li);
    if ch not in '0'..'9' then break;
    i := li;
    Result *= 10;
    Result += ch.ToDigit;
  end;
  
  Result *= k;
end;
 
var s := ReadString;
var i := 0;
 
var a := NextNum(s, i);
var op := NextSym(s, i);
var b := NextNum(s, i);
if NextSym(s, i) <> '=' then Error;
var c := NextNum(s, i);
if i<>s.Length then Error;
 
case op of
  '+': Write( if a+b=c then 'YES' else 'NO' );
  '-': Write( if a-b=c then 'YES' else 'NO' );
  '*': Write( if a*b=c then 'YES' else 'NO' );
  '/': Write( if a=c*b then 'YES' else 'NO' );
  else Error;
end;

  Halt(0);

  '/': Write( if (a=c*b) and (c<>0) then 'YES' else 'NO' );

procedure Halt;
begin
  System.Diagnostics.Process.GetCurrentProcess.Kill;
  //Halt(ExitCode);
end;
 
procedure Halt(exitCode: integer);
begin
  //System.Diagnostics.Process.GetCurrentProcess.Kill;
  //WINAPI_TerminateProcess(System.Diagnostics.Process.GetCurrentProcess.Handle, exitCode);
  System.Environment.Exit(exitCode);
end;