var test = (function(rate, limit) {
var interval_id = setInterval(function() {
  var root = document.getElementById('problems');
  var problems = root.getElementsByTagName('div');
  var wait = false;

  for (var i = 0; i < problems.length; i++) {
    var problem = problems[i];
    var costs = problem.getElementsByClassName('cost');
    var awards = problem.getElementsByClassName('award');
    var solve = problem.getElementsByTagName('a');

    //if (costs.length) {
      //if (solve.length && !wait) { solve[0].click(); }
      //else { wait = true; }
    //} else {
      if (solve.length) { solve[0].click(); }
    //}
  }
}, rate);

if (limit) {
  setTimeout(function() {
    clearInterval(interval_id);
  }, limit);
}
})(100, 10e5);