He was a welder, but he said one day his employer took his identification documents to issue work permits. He never saw the man or his papers again.
He explained that he cannot get into the city's homeless shelters at night because they are reserved for people from Moscow. He also knows people who have died from the cold, but so far he hasn't gotten frostbite.
"Thank God, not yet," he said.
Alexander comes to the mobile clinic most Wednesdays for warm food and medicine. He says they've help keep him alive.
Stanislav is luckier than most. He has been going to the same building entrance every night for two years. They don't kick him out, he explains, because he doesn't cause any trouble.
"They know me there. They don't touch me," he said.
Others, he said, are expelled from public buildings when they close for the night. He knows homeless people who disappeared after a particularly cold night.
As Dr Liza saw her last patient for the night -- a man who wanted her to inspect his ear -- Nikolai and the other volunteers packed up the van.
The crowd dispersed and Sergei, his new socks still in hand, walked off into the night.