var prim:array[1..2000000] of byte;
    i,j,k,n,nr:integer;
    f,g:text;
begin
assign(f,'ciur.in');reset(f);
assign(g,'ciur.out');rewrite(g);
readln(f,n);
for i:=2 to n do
        if prim[i]=0 then
        begin
                inc(nr);
                j:=i+i;
                while j<=n do
                begin
                        prim[j]:=1;
                        j:=j+i;
                end;

        end;

writeln(g,nr);


close(f);close(g);
end.