cố gắng giúp mk vs nhé

uses crt;
var s,s2:string;
res,i,t:longint;

function int(s:string):longint;
begin
val(s,int);
end;

begin
assign(input,'GTBT.inp');
reset(input);
assign(output,'GTBT.out');
rewrite(output); 
readln(s);
res:=0;
i:=1;
while s[i] in['0'..'9'] do
begin
 s2:=s2+s[i];
 i:=i+1;
end;
res:=int(s2);
if s[1]='-' then res:=res*-1;
s2:='';
s:=s+' ';
while s[i]<>' 'do
begin
 if s[i]='-' then t:=-1 else t:=1;
 i:=i+1;
 if (s[i]='-') or(s[i]='+') then
 begin
  res:=-1;
  break;
 end;
 while s[i] in['0'..'9'] do
 begin
  s2:=s2+s[i];
  i:=i+1;
 end;
 res:=res+(int(s2)*t);
 s2:='';
end;
if s[length(s)-1] in['0'..'9'] then
write(res) else write(-1);
readln
end.