program ciur;
type vector1=array[0..2000001] of byte;
var t:vector1;
    n,i,j,nr:longint;
    f1,f2:text;
procedure ciur(n:longint);
begin
i:=2;
while i<=n do begin
if t[i]=0 then begin
nr:=nr+1; j:=i*i;
while j<=n do begin
t[j]:=1;
j:=j+i;
end;
end;
i:=i+1;
end;
end;
begin
assign (f1,'ciur.in');
assign (f2,'ciur.out');
reset (f1);
rewrite (f2);
readln (f1,n);
nr:=0; ciur(n);
writeln (f2,nr);
close (f1);
close (f2);
end.