var a,b,c,z:longint;
begin
readln(z);
c:=3;
b:=0;
a:=0;
repeat
c:=c+1;
for a:=2 to c div 2 do
if c mod a=0 then
break
else
b:=b+1;
until c>z-2;
writeln(b);
end.