var a:array[1..2000001] of byte;
n,i,j,k,l:longint;
begin
assign(input,'ciur.in');
assign(output,'ciur.out');
reset(input);
rewrite(output);
readln(N);
fillchar(a,sizeof(a),0);
k:=0;
for i:=2 to n do
        if a[i]=0 then
                begin
                j:=i;
                while j+i<=n do
                        begin
                        inc(j,i);
                        a[j]:=1;
                        end;
                inc(K);
                end;
writeln(K);
close(input);
close(output);
end.