import sys

sys.setrecursionlimit(10 ** 6)
int1 = lambda x: int(x) - 1
p2D = lambda x: print(*x, sep="\n")
def MI(): return map(int, sys.stdin.readline().split())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]

def main():
    n,m=MI()
    aa=LI()
    cc=list(range(n,0,-1))
    for a in aa:
        c=cc.pop(-a)
        cc.append(c)
    print(cc[-1])

main()