const   tfi='ciur.in';
        tfo='ciur.out';
        maxn=2000005;
var     fi,fo:text;
        cnt, i,j,n:longint;
        dd:array[0..maxn] of byte;
begin
        assign(fi,tfi); reset(fi);
        assign(fo,tfo); rewrite(fo);
        read(fi,n);
        for i:=2 to n do
        if dd[i]=0 then
         begin
           j:=i; inc(cnt);
           while i+j<=n do
            begin
             j:=i+j; dd[j]:=1;
            end;
         end;
        writeln(fo,cnt);
        close(Fi); close(fo);
//        writeln((datetimetotimestamp(now).time-tbegin.time)/1000:0:6);
end.