program ciur;
var ciur2:array[1..64000]of byte;
    n,i,s,j:word;
    f1,f2:text;

begin
assign(f1,'ciur.in'); reset(f1);
assign(f2,'ciur.out'); rewrite(f2);
readln(f1,n);
s:=0;
for i:=1 to n do
   begin
   ciur2[i]:=1;
   end;
for i:=2 to n div 2 do
   for j:=2 to n div i do
      ciur2[i*j]:=0;
for i:=3 to n do
   if ciur2[i]=1 then
     s:=s+1;
writeln(f2,s);
close(f1);
close(f2);
end.