const main = (inputs) => {
  const array = inputs[0].split(' ');
  const A = array[0];
  const B = array[1];
  const M = Number(array[2]);

  const array_A = inputs[1].split(' ');
  const array_B = inputs[2].split(' ');
  var answer = 0;


  const minPrice_A = Math.min.apply(null, array_A);
  const minPrice_B = Math.min.apply(null, array_B);

  for (var i = 3; i < 3 + M; i++) {
    var array_M = inputs[i].split(' ');
    var price = Number(array_A[array_M[0] - 1]) + Number(array_B[array_M[1] - 1]) - Number(array_M[2]);
    if (i === 3 || price < answer) {
      answer = price;
    }
  }
  answer = answer < minPrice_A + minPrice_B ? answer : minPrice_A + minPrice_B;
  console.log(answer);
}

main(require('fs').readFileSync('/dev/stdin', 'UTF-8').trim().split("\n"));