Really?? You don't know?? Yondaime is the fourth Hokage.
Yondaime means fourth (Hokage)
It goes:
first: Shodai (Hokage)
second: Nidaime (Hokage)
third: Sandaime (Hokage)
fourth: Yondaime (Hokage)
fifth: Godaime (Hokage)
Are you watching the anime in english?? I would suggest you to watch it in japanese with english subtitles. Then you could hear Yondaime

Like always the original is way better. It makes the viewing of the anime totally differnt. I just once listened to naruto's voice on english. I really had to laughxdxdxd.
What's he saying: "Believe it!!!":flaw:
And the pronouncing of the names,

.
But you have to decide for yourself. Just a well-intentioned advise