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export function climbing_stairs_bigint(num: bigint): bigint {    if (num === 0n) return 1n;    if (num < 1) {        throw Error("must grater than one");    }    const bigInt = BigInt;    const cached = cacheClimbStairs.get(num);    if (typeof cached !== "undefined") {        return cached;    }    num = bigInt(num);    for (let e = 1n; e <= num; e++) {        if (cacheClimbStairs.has(e)) {            continue;        } else {            const r = cacheClimbStairs.get(e) ||                bigInt(                        cacheClimbStairs.get(e - 1n) ||                            climbing_stairs_bigint(e - 1n),                    ) +                    bigInt(                        cacheClimbStairs.get(e - 2n) ||                            climbing_stairs_bigint(e - 2n),                    );            cacheClimbStairs.set(e, r);        }    }    return climbing_stairs_bigint(num);}const cacheClimbStairs = new Map<bigint, bigint>([    [1n, 1n],    [2n, 2n],]);