The question is: How do you define "the coldest"? Is it the country with the lowest annual mean temperature, the lowest mean winter temperature, number of days below a certain temperature threshold etc? Antarctica would be the coldest by just about any measure but that's a continent not a country. Without doing any serious research I'd say one of the far northern European countries would be the coldest overall based on severe winters and very mild summers although northern inland Asia probably has lower extreme winter minimums but much higher summer maximums.
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