n = gets.to_i
s = gets.chomp
if n > 3
    puts "YES"
else
    yesno = n.times.find do |i|
        i.upto(n-1).find do |j|
            s[i .. j] == s[j .. 2*j-i+1]
        end
    end
    puts yesno ? "YES" : "NO"
end