var n,i,nr:longint;
    f,g:text;
function prim(x:longint):boolean;
var aux,i:word;
    g:boolean;
begin
g:=true;
aux:=trunc(sqrt(x));
for i:=2 to aux do
if x mod i=0 then g:=false;
 prim:=g;
end;
begin
assign(f,'ciur.in');reset(f);
assign(g,'ciur.out');rewrite(g);
read(f,n);
nr:=0;
for i:=2 to n do
if prim(i)=true then inc(nr);
write(g,nr);
close(f); close(g);
end.