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Hi Fatih,
According to the Kodansha's Concise Romanized Japanese-English Dictionary, "ato" （後 in kanji）has four meanings and yours is No.4 below.
1) the area behind
2) time after, time later
3) the rest, remainder
4) another, more (preceding a word that specifies a quantity)
Another example of No.4 case:
Ato gofun matte kudasai.
Please wait five more minutes.
Just for your information, there are other "ato"s in different kanji, and those are not included in the four meanings above.
For example, ato（跡） means, mark, trace, track, trail.
I hope it helps!
