program prog3;

{$APPTYPE CONSOLE}

uses
  SysUtils,
  windows;

var a:array[1..100000000] of byte;
j,k,n,i:integer;
  time:int64;


begin
readln(n);
time:=gettickcount;
a[1]:=1;
for i:=2 to round(sqrt(n)) do
begin
  if a[i]=0 then begin
  j:=i*i;
  while(j<=n)do
  begin
    a[j]:=1;
    j:=j+i;
  end;
end;
end;
{for k:=1 to n do
if a[k]=0 then write(k,' ');
writeln;
}time:=gettickcount-time;
writeln(time/1000:0:5);

readln;
  { TODO -oUser -cConsole Main : Insert code here }
end.