{ Ciurul lui Eratosthenes }
type vector=array[1..2000000] of byte;

var v:vector;
    f:text;
    i,j,n,k:longint;

begin
     Assign(f,'ciur.in'); reset(f); read(f,n); close(f);
     Assign(f,'ciur.out'); rewrite(f);
     k:=0;
     v[1]:=1;
     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.