program ciur;   
var f,g:text;   
    i,j,n,k,s:longint;   
    a:array[1..60000]of byte;
begin  
assign(f,'ciur.in');reset(f);   
assign(g,'ciur.out');rewrite(g);   
readln(f,n);   
s:=0;   
for i:=2 to n  do  
    if a[i]=0 then begin  
                   k:=i;   
                   s:=s+1;   
                   for j:=2 to n div k do a[j*k]:=1;   
  
                   end;   
writeln(g,s);   
close(f);
close(g);   
end.