fast_track.js

function (input) {
  var numbers_to_product = 5;
  var max = 0;
 
  for (var i = 0; i <= input.length - numbers_to_product; i++) {
    var product = _.reduce(_.range(i, i + numbers_to_product), function(acc, j) {
      return acc * parseInt(input[j]);
    }, 1);
  
    if (product > max) {
      max = product;
    }
  }
 
  return max;
}