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Hello Nikita,
Well, in this case the difference with a male Platycheirus clypeatus lays in the color of the antenna. In P. clypeatus the third segment is black, and in Melanostoma mellinum this third segment is largely yellow.
If you look at your picture, it is clearly visible that this segment is partially yellow. So that is why I said a male of Melanostoma mellinum!
Greetings,