const
SIZE=100;
Var
P:array [1..SIZE] of integer;
N,tot,cn,i:integer;
Begin
Readln(n);
For i:=1 to n do
P[i]:=1;
Tot:=0;
For i:=2 to n do
Begin
If p[i]=1 then
Tot:= tot +1;
cn:=i*2;
While cn<=n do
Begin
P[cn]:=0;
cn:=cn+i;
End;
End;
Writeln(tot);
End.
输入：30；
输出：10