Ok first of all, NONE of the russian nukes come even close to 50-100 megatons. The TSAR bomba the largest nuke EVER build and used was 50 megaton, it was so big that it would be impossible to launch it with any rocket that russia has.
No country on earth has any nukes that come even close to that 100 megaton yield.
The biggest nuke that the US have ever tested and made was 15 megatons (Castle Bravo).
The largest bomb currently in service in the U.S. nuclear arsenal is the B83, with a maximum yield of 1.2 megatons.