var exposure = 20;
var input_index = 0;

function setpic() {
  $("#pic").attr("src", exposure + "/" + files[input_index]);
}

$(function() {
  setpic();
});

Mousetrap.bind('z', function() { $("#pic").toggleClass("fit_view"); });
Mousetrap.bind('n', function() { input_index ++; setpic(); });
Mousetrap.bind('p', function() { input_index --; setpic(); });