Quoting Henrik Meinander in Finland in World War II: History, Memory, Interpretations, page 60:

Equally important was that the Soviet units were usually led by weakly trained army commanders, who were forced to follow extraordinary orders from their political officers. But from February 1940 onwards, the greatly increased Soviet superiority in the number of troops and weaponry became decisive.

When the Red Army reached the outskirts of the city of Vyborg in early March, the Finnish government was ripe for peace. After a feverish negotiation process, the states signed a peace treaty in Moscow on 13 March 1940, in which the Karelian Isthmus, Ladoga Karelia, Salla region and the northern tip of the Pechenga region became Soviet territories.

[…]

The human losses were also severe. Almost 28,000 Finns (about 27,000 soldiers and 1,000 civilians) died in the war.

Thereby the 105‐days long Winter War had come to an end.

(Emphasis added.)

That’s really all that I wanted to say.