import sys

sys.setrecursionlimit(200005)
int1 = lambda x: int(x)-1
pDB = lambda *x: print(*x, end="\n", file=sys.stderr)
p2D = lambda x: print(*x, sep="\n", end="\n\n", file=sys.stderr)
def II(): return int(sys.stdin.readline())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def LI1(): return list(map(int1, sys.stdin.readline().split()))
def LLI1(rows_number): return [LI1() for _ in range(rows_number)]
def SI(): return sys.stdin.readline().rstrip()
dij = [(0, 1), (-1, 0), (0, -1), (1, 0)]
# dij = [(0, 1), (-1, 0), (0, -1), (1, 0), (1, 1), (1, -1), (-1, 1), (-1, -1)]
inf = 18446744073709551615
# inf = 4294967295
# md = 10**9+7
# md = 998244353
md = 10**8+9

def is4():
    if m == 0: return n & 1 == 0
    if s == -1: return False
    u = s
    while 1:
        v = to[u]
        d = v-u
        if d < 0: d += n
        if v == -1: return False
        if d & 1 == 0: return False
        if v == s: return True
        u = v

n, m = LI()

to = [-1]*n
s = -1
for _ in range(m):
    u, v = LI1()
    if to[u] == -1:
        to[u] = v
    else:
        to[u], to[max(to[u], v)] = min(to[u], v), u
        s = u

print(4 if is4() else 5)