n,m = map(int,input().split())
num = [-1]*n
for i in range(m):
  s,c = map(int,input().split())
  if n!=1 and s==1 and c==0:
    print(-1)
    exit()
  if num[s-1]==-1: num[s-1] = c
  elif num[s-1]!=c:
    print(-1)
    eixt()
for i in range(n):
  if num[i] = -1: num[i] = 0
if num[0] = 0 and len(num)!=1: num[0] = 1
print(int(''.join(num)))
