Program giup;

Uses crt;

Var a,b,i,s:longint;

Function ngto(m:longint):bolean;

Var i:longint;

Begin

Ngto:=true;

If m<=1 then ngto:=false

Else

 For i:=2 to m div 2 do

   If m mod i=0 then ngto:=false;

End;

Begin

Write('nhap A,B: '); readln(a,b); s:=0;

For i:=a to b do

 If Ngto(i) then s:=s+i;

Write('tong cac so nguyen to tu ',a,' den ',b,' la: ',s);

Readln;

End.

program bai_giai;
uses crt;
var a,b,i,t:longint;
function ktnt(k:longint):boolean;
var r:longint;
begin
    ktnt:=false;
    if k<2 then exit;
    for r:=2 to trunc(sqrt(k)) do
        if k mod r=0 then exit;
    exit(true);
end;
BEGIN
    clrscr;
    write('Nhap a: ');  readln(a);
    write('Nhap b: ');  readln(b);
    t:=0;
    for i:=a to b do
        if ktnt(i) then t:=t+i;
    write(t);
    readln;
end.