{ Ciurul lui Eratosthenes }
type vector = array [1..2000000] of byte;
var f:text;
    i,j,n,k:integer;
    v:vector;

begin
        Assign(f,'ciur.in'); reset(f);
        Read(f,n); close(f);
        Assign(f,'ciur.out'); rewrite(f);
        k:=0;
        For i:=1 to trunc(sqrt(n)) do
            if v[i]=0 then
               for j:=2 to n div i do
                   v[i*j]:=1;
        For i:=2 to n do
            if v[i]=0 then Inc(k);
        write(f,k);
        close(f);
end.