const MAX=1000000000;
var del: array[2..MAX] of boolean;
n,p,i,k,r,j:longint;
function ciurul(n:qword):qword;
var i,j:longint;
begin
    for i:=2 to n do del[i]:=false;
    i:=2;
    repeat
      if not del[i] then begin
        j:=i*i;
        while j<=n do begin
          del[j]:=true;
          j:=j+i;
        end;
      end;
      i:=i+1;
    until i*i>n;
    for i:=2 to n do if not del[i] then r:=r+1;
    ciurul:=r;
end;
begin
    assign(input,'ciur.in');
    assign(output,'ciur.out');
    reset(input);
    rewrite(output);
    read(n);
    r:=ciurul(n);
    write(r);
    close(input);
    close(output);
end.