We investigate a performance of cooperative relaying in the device-to-device (D2D) systems underlaying cellular networks while considering power constraints on the average received-interference at the evolved NodeB (eNB). Specifically, we consider the D2D communication assisted by relays using multihop decode-and-forward (DF) strategy in interference existing circumstances. In this paper, we obtain exact closed-form expression for the CDF and the PDF of the received Signal-to-Interference-plus-noise ratio (SINR) at the end user over Rayleigh flat fading channel. The end-to-end performance is investigated in terms of the maximum ergodic capacity, and the outage probability. Simulation results follow to show the performance of the system in the various propagation conditions.