n, m = map(int, input().split())


ans = [-1 for _ in range(n)]
for i in range(m):
  s, c = map(int, input().split())
  if ans[s-1] != c and ans[s-1] != -1:
    print(-1)
    exit()
  else:
    ans[s-1] = c
    
if ans[0]==0:
  print(-1)
  exit()
  
if ans[0]==-1:
  ans[0] = 1

for i in range(1,n):
  if ans[i]==-1:
    ans[i] = 0
  
print(*ans, sep='')
