const fi='tongnto.inp';

         fo='tongnto.oup';

var f:text;

      a,b,i,s:longint;

funtion nt(x:longint):boolean;

var i:longint;

begin

nt:=false;

if x<2 then exit;

for i:=1 to x div 2 do

if x mod i=0 then exit;

nt:=true;

end;

begin

assign(f,fi);reset(f);readln(a,b);close(f);

assign(f,fo);rewrite(f);

if (a<2) or (a>b) then write(f,'Du lieu vao khong xac dinh')

else

  begin

  s:=0;

  for i:=a to b do

  if nt(i)=true then s:=s+i;

  write(f,s);

  end;

close(f);

end.

var   a,b: integer;
    s,i: integer;
    f1,f2: text;
Function nt(n:integer):boolean;
var i:integer;
begin
nt:=false;
for i:=2 to trunc(sqrt(n)) do
if n mod i=0 then exit;
if n<2 then exit;
nt:=true;
end;
begin
assign(f1,'tongnto.inp');
reset(f1);
assign(f2,'tongnto.out');
rewrite(f2);
repeat
readln(f1,a,b);
until (a>=2) and (a<b);
s:=0;
for i:=a to b do 
if nt(i) then s:=s+i;
write(f2,'tong: ',s);
close(f1); close(f2);
end.