N,M = map(int,input().split())
graph = [[] for i in range(N)]
p = [list(map(int,input().split())) for i in range(M)]
p = sorted(p,reverse=True)
ans = 0
s = set()
for i in range(M):
	if p[i][1] in s:
		continue
	s.add(p[i][0])
for i in s:
	ans += (1<<i)
print(format(ans,'b'))