This a small coin, 15mm, 1.70g.
The obverse has a very nice buts I can read the DN CONSTAN. But the second part of the legend fell mostly outside the disk.

The mint mark may be V, then NN
The reverse legend end in EXERC ITVS, so GLORIA EXERCITVS
I could remove the green copper oxides in the reverse. But they are nice and stable.
Can someone tell which emperor was this?