program Ciurul_Lui_Eratostene;
var n,i,j,nr:longint;
    v:array[1..2000000] of boolean;
    f,g:text;
begin
assign(f,'ciur.in');
assign(g,'ciur.out');
reset(f);
nr:=0;
read(f,n);
close(f);
for i:=1 to n do
 v[i]:=true;

// nr:=n-1;  // scad numarul 1 deoarece nu e prim
for i:=2 to n do
   if v[i]=true then
                 for j:=2 to n div i do begin
                      //if v[i*j]=true then nr:=nr-1;
                         v[i*j]:=false;

                                        end;
for i:=1 to n do
 if v[i]=true then nr:=nr+1;

rewrite(g);
write(g,nr-1);
close(g);
readln
end.