606 B | 606 chars
import sys
from math import sqrt, pi, sin, factorial
BLANK = " "
inp = lambda : sys.stdin.readline()[:-1].strip()
mii = lambda x = BLANK : [*map(int,inp().split(x))]
mfi = lambda x = BLANK : [*map(float,inp().split(x))]
ii = lambda : int(inp())
fi = lambda : float(inp())
p = print
def solve():
n, m = mii()
l = [ii() for _ in range(m)][::-1]
for i in range(1, n + 1):
crt = i
for leg in l:
if crt == leg:
crt = leg + 1
elif crt == leg + 1:
crt = leg
print(crt)
if __name__ == "__main__":
tc = 1
for t in range(1, tc+1):
ret = solve()