#! ruby
# yukicoder My Practice
# author: Leornadone @ NEETSDKASU

(N, M), A = $<.map{|x| x.chomp.split.map(&:to_i)}

card_top = [0, []]
ref = card_top
1.upto(N) do |i|
	ref[1] = [i, []]
	ref = ref[1]
end

A.each do |ai|
	ref = card_top
	ai.pred.times do
		ref = ref[1]
	end
	new_top = ref[1]
	ref[1] = new_top[1]
	new_top[1] = card_top[1]
	card_top[1] = new_top
end

puts card_top[1][0]