program ciur;
var n,i,j,k:integer;
   a:array[1..1000000] of boolean;
   fi,fo:text;
begin
assign(fi,'ciur.in');reset(fi);
assign(fo,'ciur.out');rewrite(fo);
read(fi,n);
for i:=1 to n do a[i]:=true;
for i:=2 to n do
               if a[i] then   for j:=2 to n div i do a[i*j]:=false;
for i:=2 to n do
              if a[i] then  inc(k);write(fo,k);
close(fi);close(fo);
end.