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Probably it's "Много лет"(without o at the end), but I don't know this song.

There's also a translation of the English "Happy birthday" (but often people sing it in English too)
С днём рожденья тебя,
C днём рожденья тебя.
С днём рожденья, с днём рожденья.
С днём рожденья...