program eraszthotenesz;
var n,i,j,p,sz:longint;
 a:array[1..2000000] of boolean;
 f,g:text;
Begin sz:=0;
assign(f,'ciur.in');
assign(g,'ciur.out');
reset(f);rewrite(g);
readln(f,n); close(f);
a[1]:=false;
for i:=2 to n do a[i]:=true;
p:=2;
while p*p <= n do begin
 j:=p*p;
 while (j<= n) do begin
 a[j]:=false;
 j:=j+p;
 end;
  repeat p:=p+1 until a[p]=true;
end;
assign(f,'prim.out');  rewrite(f);
 for i:=1 to n do if a[i]=true then inc(sz);
 write(g,sz);
close(f);close(g);
End.