def get_unique_list(seq):
    seen = []
    return [x for x in seq if x not in seen and not seen.append(x)]
            
a,o=map(int,input().split())
l=[list(map(int,input().split())) for i in range(o)]
g = get_unique_list(l)
c = sorted(g)
d = 0
b = len(c)
if c[0] == [1,0]:
 print(-1)
else:
 for k in range(b-1):
  if l[k][0] == l[k+1][0]:
   print(-1)
   break
 else:
  for j in range(b):
   if a < c[j][0]:
    print(-1)
    break
   d=d+(10**(a-c[j][0]))*c[j][1]
  else:
   print(d)