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var SmallestInfiniteSet = function () {
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  const s = new Set();
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  this.s = s;
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  for (let i = 1; i <= 1000; i++) s.add(i);
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};
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/**
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 * @return {number}
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 */
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SmallestInfiniteSet.prototype.popSmallest = function () {
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  const min = Math.min(...Array.from(this.s));
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  this.s.delete(min);
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  return min;
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};
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/**
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 * @param {number} num
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 * @return {void}
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 */
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SmallestInfiniteSet.prototype.addBack = function (num) {
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  this.s.add(num);
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};
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/**
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 * Your SmallestInfiniteSet object will be instantiated and called as such:
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 * var obj = new SmallestInfiniteSet()
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 * var param_1 = obj.popSmallest()
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 * obj.addBack(num)
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 */