Code:
var
i,l,a,b,max,z,d:integer;
otvet:string;
x,y:array[1..50000]of integer;
bo:boolean;
begin
bo:=true;
readln(a);
if (a>=1)and(a<=50000) then
begin
for i:=1 to a do
begin
readln(x[i]);
end;
readln(b);
for i:=1 to b do
begin
readln(y[i]);
end;
if a>b then max:=a;
if b>a then max:=b;
for i:=1 to max do
begin
if bo=true then
begin
for l:=1 to max do
begin
z:=x[i]+y[l];
if z=10000 then
begin
d:=1;
bo:=false;
end;
end;
end;
end;
if d=1 then otvet:='YES'
else otvet:='NO';
write(otvet);
end;
end.
BECAUSE ERROR?

Because you are must use
if a>=b then max:=a;
if b>a then max:=b;