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require 'prime' require 'date' n = gets.to_i+1 a = [0] (Date.parse("19700101")..Date.parse("20191231")).each{|i| a[-1]+=1;a << 0 if i.to_s.gsub(?-,"").to_i.prime? } m = t = a[0...n].inject(:+) (a.size-n).times{|i| m=[t+=a[i+n]-a[i],m].max } p m-1
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