N,M=map(int,input().split())#N桁M条件
A=[0 for _ in range(N)]
for _ in range(M):
  s,c=map(int,input().split())#左からs番目がc
  if s==1 and c==0:
    print(-1)
    exit()
  elif A[s-1]==0:
    A[s-1]=c
  elif A[s-1]==c:
    pass
  elif s==1 and c==0:
    print(-1)
    exit()
  else:
    print(-1)
    exit()
if A[0]==0:
  A[0]=1
a=0
for i in range(N):
  a+=A[i]*10**(N-1-i)
print(a)