(function(document) {
  var json   = document.getElementsByTagName('pre')[0].innerText
  var obj    = JSON.parse(json)
  var cards  = obj.cards
  var output = 0

  cards.map(function(card, index) {
    var pre = card.name.indexOf('[') + 1
    var post = card.name.indexOf(']') -1
    var value = card.name.substr(pre, post)

    if (value && !isNaN(value)) {
      output += parseFloat(value)
    }
  })

  console.log(output)
})(document)