n,m=map(int,input().split())
l=[]
for i in range(m):
  a,b=map(int,input().split())
  l.append([a,b])
for i in range(10**(n-1)-1,10**n):
  x=str(i)
  c=0
  for i in range(m):
    if x[l[i][0]-1]==str(l[i][1]):
      c+=1
  if c==m:
    print(x)
    quit()
print(-1)