Is it okay to wear a pair of warm pants and a thin sweater when traveling to Russia?

Absolutely not. At present, the average temperature in Russia is about 22 degrees white, about 12 degrees late, and it will be even colder in a few days. I suggest you bring clothes in late autumn or early winter. Another solution is to choose a warmer coat so that you can wear less inside. The climate in Russia is 1 month ahead of the domestic winter solar terms, and 1 month ahead.