var v:array[1..1000000] of byte;
    i,j,k:longint;
begin
assign(input,'ciur.in'); reset(input);
assign(output,'ciur.out');rewrite(output);
readln(k);
for i:=2 to trunc(sqrt(k)) do
 if v[i]=0 then for j:=2 to k div i do v[i*j]:=1;
j:=0;
for i:=2 to k-1 do
if v[i]=0 then inc(j);
writeln(j);
close(input); close(output);
end.