n,m=map(int,input().split())
e={i:set() for i in range(n)} 
a=set()
for _ in range(m):
    s,l=map(int,input().split())
    e[l].add(s)
for i in range(n-1, -1, -1):
    if i not in a:a|=e[i]
r=0
for i in a:r|=1<<i
print(format(r, 'b'))