用pascal计算a+b的和！急！急！

program circle;
var
a,b,c:longint;
begin
read(a,b);
c:=a+b;
write(c);
end.
a+b太大只能
program circle;
var
s2,s3:string;
a,b:array[1..100] of integer;
k,l2,l3,i,j:integer;
begin
read(s2,s3);
l2:=length(s2);
l3:=length(s3);
if l2>l3 then j:=l2
else j:=l3;
k:=0;
for i:=l2 downto 1 do
begin
k:=k+1;
.......................................

高精度算法

用int64数据类型处理大数据。。。。
program ab;
var
a,b:int64;
begin
readln(a,b);
a:=a+b;
writeln(a);
end.