function stringy(num) {
  var result = [1];

  if (num == 1) { return result; };

  for(i = 0; i < num; i++) {
    var lastElement = result[result.length - 1];

    lastElement == 0 ? result.push(1) : result.push(0);
  }

  return result.join("").substring(0, num);
};

console.log(stringy(4));