var i,j,n:longint;
    f,g:text;
function prim(i:integer):boolean;
var j:integer;
    b:boolean;
begin
j:=2;
while (j<=i div 2)and b do
begin
 b:=i mod j<>0;
 j:=j+1;
end;
prim:=b;
end;
begin
assign(f,'ciur.in');
assign(g,'ciur.out');
reset(f);
rewrite(g);
read(f,n);
i:=3;
j:=1;
while i<=n do
begin
 if prim(i) then j:=j+1;
 i:=i+2;
end;
write(g,j);
close(f);
close(g);
end.