function Main (input) {
  input = input.split("\n").map(inp => inp.split(" ").map(inp2 => parseInt(inp2, 10)));
  var A = input[0][0];
  var B = input[0][1];
  var M = input[0][2];
  var a = input[1];
  var b = input[2];
  input.shift();
  input.shift();
  input.shift();
  input.pop();
  var x = input;
  var kh = [];
  
  for (var i of x) {
    kh.unshift((a[i[0]-1]+b[i[1]-1]) - i[2]);
  }
  console.log(Math.min(...a) + Math.min(...b) < Math.min(...kh) ? Math.min(...a) + Math.min(...b) : Math.min(...kh))
}

Main(require("fs").readFileSync("/dev/stdin", "utf8"));