program Ciurul_Lui_Eratostene;
var n,i,j,nr:longint;
    v:array[1..2000000] of boolean;
    f,g:text;
begin
assign(f,'ciur.in');
assign(g,'ciur.out');
reset(f);
nr:=0;
read(f,n);
close(f);
for i:=1 to n do
 v[i]:=true;

for i:=2 to n do
  for j:=2 to n div i do
   v[i*j]:=false;
for i:=2 to n do
 if v[i]=true then nr:=nr+1;
rewrite(g);
write(g,nr);
close(g);
readln
end.