program ciur;
type vector=array[1..2000005] of 0..1;
var v:vector;
    n,cnt,i,j:longint;
    f,g:text;
begin
assign(f,'ciur.in');reset(f);
assign(g,'ciur.out');rewrite(g);
read(f,n);
for i:=2 to n do v[i]:=1;
for i:=2 to n do if v[i]=1 then for j:=2 to n div i do v[i*j]:=0;
cnt:=0;
for i:=2 to n do if v[i]=1 then inc(cnt);
writeln(g,cnt);
{for i:=1 to n do if v[i]=1 then write(g,i,' ');}
close(f);close(g);
end.