var f,g:text;
    i,n,nr,j:longint;
    a:array[1..2000000]of byte;
begin
assign(f,'ciur.in');
assign(g,'ciur.out');
reset(f);
rewrite(g);
read(f,n);
for i:=1 to n do
a[i]:=1;
for i:=2 to trunc(sqrt(n)) do
if a[i]=1 then
begin
for j:=i to (n div i) do
a[i*j]:=0;
end;
nr:=0;
for i:=1 to n do
if a[i]=1 then nr:=nr+1;
writeln(g,nr-1);
close(f);
close(g);
end.