And there was a famine in the days of David for three years [(Shmuel Bet 21)]. And in Pirkei Avot chapter 17: after the year when Shaul destroyed [Nov], there was the famine. And Rashi on Yevamot 78b, 79a [says] that this was close to thirty years after the death of Shaul. And in Yalkut: after three years.

And in Gilayon it is printed thirty years.