program ciur;
var f,g:text;
    n,nr,j,i:longint;
    prim:array[1..10000]of longint;
begin
assign(f,'ciur.in');reset(f);
assign(g,'ciur.out');rewrite(g);
read(f,n);
for i:=2 to n do
    prim[i]:=1;
for i:=2 to n do
    if prim[i]=1 then
       begin
       inc(nr);
       j:=i+i;
       repeat
        prim[j]:=0;
        j:=j+i;
       until j>n;
       end;
writeln(g,nr);
close(g);
close(f);
end.