1. All of the plaintiffs' claims are dismissed.

2. The costs of lawsuit are assessed against the plaintiffs.

1. The following facts may be found either in dispute between the parties or in full view of the entries in Gap evidence 1, Eul evidence 3 and 5 and all the arguments.

On June 2010, Plaintiffs, D, and E agreed to newly construct and distribute officetels on the above land (hereinafter “J”) after investing in the F, G, H, and I land in Mapo-gu Seoul, Mapo-gu, Seoul, H, H, and I.

B. Around October 9, 2012, D specified the period of construction from October 10, 2012 to December 10, 2012, 840,000 won for construction work (excluding value-added tax) to the Defendant.

C. D and the Defendant agreed on April 25, 2013 to increase the price of the instant construction project from KRW 840,000,000 to KRW 85,000,000, which was the first agreed upon on April 25, 2013 (excluding value-added tax).

2. The assertion and determination Plaintiffs asserted that the Defendant received KRW 1,017,50,000 from the Plaintiffs regarding the instant construction project (i.e., KRW 925,00,000 value-added tax of KRW 92,50,000), but in fact, the Plaintiffs asserted that the Defendant should return the difference to the Plaintiffs on the ground that the Plaintiff obtained unjust enrichment equivalent to KRW 63,958,40,00, which is the difference, by simply doing the construction work equivalent to KRW 953,541,60.

On the other hand, the plaintiffs' assertion purport that the defendant's unjust enrichment should be acquired and returned because the defendant unfairly agreed the construction cost of the construction of the construction of this case. ① Unless the construction cost agreement is invalidated, the receipt of the construction cost pursuant to the agreement cannot be deemed as unjust enrichment, and the contract cannot be invalidated on the ground that the agreed construction cost is more objectively reasonable than the construction cost, so the above assertion is without merit. ② In addition, according to the above basic facts, the contractor of the construction of this case is not the plaintiffs, but D, and the evidence submitted by the plaintiffs is alone.