import sequtils,strutils,algorithm
var
    N, M : int
    A : seq[int]
    p : int
(N, M) = stdin.readline.split.map(parseInt)
A = stdin.readline.split.map(parseInt)
var B = newSeq[int](N)
for n in 0..<N:
    B[n] = N - n
for a in A:
    B.add(B[N - a])
    B.delete(N - a)
echo B[^1]