var p:array[1..100000] of boolean;
    n,nr:longint;

function ciur(n:longint):longint;
var nr,i,j:longint;
begin
nr:=1; i:=1;
while 2*i*i+2*i<=n do
      begin
      if p[i]=false then
         begin
         j:=2*i*i+2*i;
         while 2*j+1<=n do
               begin
               p[j]:=true;
               j:=j+2*i+1;
               end;
         end;
      inc(i);
      end;
i:=1;
while 2*i+1<=n do
            begin
            if p[i]=false then inc(nr);
            inc(i);
            end;
ciur:=nr;

end;



begin
assign(input,'ciur.in');reset(input);
assign(output,'ciur.out');rewrite(output);
readln(n);
nr:=ciur(n);
writeln(nr);
close(output);
end.