var x,n,k,i:longint;  a:array[1..20000000] of byte; f,g:text;   
begin  
assign(f,'ciur.in'); reset(f);   
readln(f,n); close(f);   
for i:=1 to n do  
a[i]:=1;   
a[1]:=0;   
for i:=2 to n do  
if (a[i]=1) then  
 begin  
  x:=2*i;   
  k:=k+1;   
  while x<=n do  
  begin  
  a[x]:=0;   
  x:=x+i;   
  end;   
 end;   
assign(g,'ciur.out'); rewrite(g);   
writeln(g,k); close(g);   
end.