var n,i,j,nr:longint;
    v:array[1..2000000] of 0..1;
    f:text;
begin
assign(f,'ciur.in');reset(f);
read(f,n);
close(f);
v[2]:=1;
for i:=3 to n do v[i]:=1;
i:=3;
nr:=1;
while i<=n do begin
              if v[i]=1 then begin
                             inc(nr);
                             for j:=2 to n div i do v[j*i]:=0;
                             end;
              i:=i+2;
              end;
assign(f,'ciur.out');rewrite(f);
writeln(f,nr);
close(f);
end.