761 B | 761 chars
import sys
from math import sqrt, pi, sin, factorial, ceil, floor
from datetime import datetime, timedelta
# sys.setrecursionlimit(10**7)
BLANK = " "
# inp = input
inp = lambda : sys.stdin.readline().rstrip()
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, Q = mii()
l = [ii() for _ in range(Q)]
d = [0] * N
cnt = 0
for i in range(N):
if i % 10 in [0, 3, 6]:
d[i] = True
cnt += 1
for i in l:
i -= 1
if d[i]:
cnt -= 1
else:
cnt += 1
d[i] = not d[i]
p(cnt)
if __name__ == "__main__":
tc = 1
for t in range(1, tc+1):
ret = solve()