
object Main extends App {
  val sc = new java.util.Scanner(System.in) 
  val A = sc.nextInt()
  val B = sc.nextInt()
  val M = sc.nextInt()  
  sc.useDelimiter("\n")
  val a = sc.next().split(" ").map(_.toInt).toList 
  val b = sc.next().split(" ").map(_.toInt).toList 
  val m = for(i <- 1 to M) yield sc.next().split(" ").map(_.toInt).toList  
  var ans = a.min + b.min
  for (i <- 0 until M) {
    val price = a(m(i)(0)-1) + b(m(i)(1)-1) - m(i)(2)
    ans = ans.min(price)
  }
  println(ans)
}