program mas;
const n=1000;
var
  m: array[1..n]of real;
  s: real;
  i: integer;
 
function prostoe(x:integer):boolean;
var
  k: integer;
begin
  result:=true;
  for k:=2 to round(x/2) do
    if x mod k=0 then
    begin
      result:=false;
      break;
    end;
end;
 
begin
  cls;
  for i:=1 to n do
    m[i]:=random(10000)/(1+random(10000));
  s:=0;
  for i:=1 to n do
    if prostoe(i) then
      s:=s+m[i];
  writeln(s);
end.