var    x,p,n,i:longword;
       pd:array[1..2000000]of boolean;
begin

assign(input,'ciur.in');
assign(output,'ciur.out');

reset(input);
read(n);
close(input);
p:=0;

for i:=1 to n do
pd[i]:=true;

for i:=2 to n do
begin

        if pd[i] then
        begin
                x:=i*i;
                p:=p+1;
                while x<=n do
                begin
                        pd[x]:=false;
                        x:=x+i;

                end;
        end;

end;



rewrite(output);
write(p);
close(output);

end.