Program ciur;
const max= 2000000;
var n,i,j,k:longint;
    prim:array [2..max] of boolean;
    fi,fo:text;

begin
assign(fi,'ciur.in');
assign(fo,'ciur.out');
reset(fi);
rewrite(fo);
     k:=0;
while not eoln(fi) do readln(fi,n);
for i:=2 to n do
prim[i]:=true;
for i:=2 to n do
begin
 if(prim[i]) then
 begin
 inc(k);
 for j:=2 to trunc (n div i) do
 prim[i*j]:=false;
 end;
 end;
 writeln (fo,k);
close(fo);
 end.