program prime is 
	var num,divisor : integer; 
	var done : boolean; 
begin
	read num; 
	while num>0 do 
	      divisor := 2; done := false; 
	      while divisor<= num/2 and not(done) do 
		    done := num = divisor*(num/divisor); 
		    divisor := divisor+1 
		    end while; 
	      if done then write 0 
		      else write num 
              end if; 
              read num 
	end while 
end