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.