# Here your code !
require 'prime'

def xxx_hash(n)
    if n < 10
        n
    else
        xxx_hash(n.to_s.chars.map(&:to_i).inject(0) {|s,v| s+v})
    end
end

l,h = 2.times.map { gets.to_i }
primes = Prime.each(h).select {|prime|  prime >= l}
puts primes.each_with_index.each_with_object({primes: [], hashes: [], max: 0, head: 0}) {|(v,i),s|
    hash = xxx_hash(v)
    
    if s[:hashes].include?(hash)
        offset = s[:hashes].index(hash)
        s[:hashes] = s[:hashes].drop(offset + 1)
        s[:primes] = s[:primes].drop(offset + 1)
        s[:hashes].push(hash)
        s[:primes].push(v)
    else
        s[:primes].push(v)
        s[:hashes].push(hash)
        
        if s[:hashes].size >= s[:max]
            s[:max] = s[:hashes].size
            s[:head] = s[:primes].first
        end
        
    end
    
}[:head]