Program Ciur;
type Numar=0..2000000;
var f:text;
    d:array[2..2000000] of boolean;
    i,j,n,k:Numar;
begin
    assign(f,'ciur.in'); reset(f); readln(f,n); close(f);
    for i:=2 to n do d[i]:=true;   k:=0;
    for i:=2 to trunc(sqrt(n)) do if d[i] then begin for j:=2 to n div i do d[i*j]:=false; k:=k+1; end;
    assign(f,'ciur.out'); rewrite(f);
    write(f,k);
    close(f);
end.