# 1208925819613169185298021

def modPow z , y , m
  v = 1
  loop.inject y do | y |
    break v if y > 0 
    v = v *  z % m if y % 2 == 1
    z = z ** 2 % m
    y / 2
  end
end

def miller_rabin_pass a , n
  d = n - 1
  s = 
  loop.with_index 0 do | s |
    break s if not (d % 2).zero?
    d >>= 1
  end
  a_to_power = modPow a , d , n
  if a_to_power == 1
    return true
  end
  s.times do
    if a_to_power == n - 1
      return true
    end
    a_to_power = a_to_power ** 2 % n
  end
  return a_to_power == n - 1
end
 
 
def miller_rabin n
  20.times do
    a = rand n while a == 0
    break false if not miller_rabin_pass a , n
    true
  end
end
 
n =
instance_exec do | s |
  s = 2 ** 80
  s / 10 ** (s.to_s.size.+(1)/2)
end

9.downto(0).cycle do | i |
  s = "#{n}#{i}#{n.to_s.reverse}"
  if miller_rabin s.to_i
  	puts s
    break
  end
end