uses crt;
var n,i,s:longint;
function prime(n:longint):boolean;
var i:longint;
begin
prime:=true;
for i:=2 to round(sqrt(n)) do if n mod i=0 then
begin
prime:=false;
break;
end;
end;
begin
clrscr;
write('N -> ');
readln(n);
s:=0;
for i:=2 to n do if prime(i) then s:=s+i;
writeln('S=',s);
readln;
end.