import itertools
import math
import sys
import heapq
from collections import Counter
from collections import deque
from fractions import gcd
from functools import reduce
sys.setrecursionlimit(4100000)
from functools import lru_cache
INF = 1 << 60

#ここから書き始める
n, m = map(int, input().split())
num = [-1 for i in range(n)]
for i in range(m):
    s, c = map(int, input().split())
    if s == 1 and c == 0:
        print(-1)
        sys.exit()
    if num[s - 1] != -1 and num[s - 1] != c:
        print(-1)
        sys.exit()
    num[s - 1] = c
# print(num)
ans = ""
for i in range(n):
    if num[i] != -1:
        ans += str(num[i])
    else:
        if i == 0:
            ans += "1"
        else:
            ans += "0"
print(ans)
