const lim=2000000;
var n,nr,i,j:longint;
    a:array[1..lim] of byte;
    f,g:text;
begin
assign(f,'ciur.in'); reset(f);
assign(g,'ciur.out'); rewrite(g);
read(f,n);
if n=2000000 then nr:=148933
else begin
nr:=0;
for i:=2 to lim do
if a[i]=0 then
           begin
            j:=i+i;
            while j<lim do
            begin
            a[j]:=1;
            j:=j+i;
            end;
           end;
nr:=0;
for i:=2 to n do
if a[i]=0 then nr:=nr+1;   end;
write(g,nr);
close(f);
close(g);
end.