We propose a new NAND programming scheme called the lazy reprogramming scheme (LazyRS) which divides a program operation into two stages, where the second stage is delayed until it is needed. LazyRS optimizes the program latency by skipping the second stage if it is not required. An idle interval before the second stage improves the flash reliability as well. To maximize the benefit of LazyRS, a LazyRS-aware FTL adjusts the length of an idle interval dynamically over changing workload characteristics. The experimental results show that the LazyRS-aware FTL can efficiently improve the write throughput and reliability of flash-based storage systems by up to 2.6 times and 31.2%, respectively.