n,m = map(int,input().split())
a = [list(map(int,input().split())) for raw in range(m)]
b = sorted(a)
ans = 0
if (b[0])[0] != 1:
  ans += 10**(n-1)
t = 0
u = -1
che = 0
for hoge in b:
  x = hoge[0]
  y = hoge[1]
  if x == 1 and y == 0:
    che += 1
  if x != t:
    ans += y*(10**(n-x))
  if x == t and y != u:
    che +=1
  t = x
  u = y
if che == 0 and ans !=0:
  print(ans)
elif che == 0 and n == 1:
  print(0)
else:
  print(-1)