from collections import defaultdict, deque, Counter
from heapq import heappush, heappop
from itertools import permutations, accumulate
from math import sqrt, ceil, floor, factorial
from bisect import bisect_left, bisect_right
from copy import deepcopy
from operator import itemgetter
from fractions import gcd
import sys
def I(): return int(input())  # '123' -> 123
def Is(): return map(int, input().split())  # '123 456' -> 123, 456
def LI(): return list(map(int, input().split()))  # '123 456' -> [123, 456]
def TI(): return tuple(map(int, input().split()))  # '123 456' -> (123, 456)
def IR(n): return [I() for _ in range(n)]
def LIR(n): return [LI() for _ in range(n)]
def TIR(n): return [TI() for _ in range(n)]
def S(): return input()
def Ss(): return input().split()  # 'aa bb' -> 'aa','bb' or ['aa','bb']
def LS(): return list(input())  # 'abc123' -> ['a','b','c','1','2','3']
def SR(n): return [S() for _ in range(n)]
def SsR(n): return [Ss() for _ in range(n)]
def LSR(n): return [LS() for _ in range(n)]
sys.setrecursionlimit(1000000)
MOD = 1000000007
INF = float('inf')

n, m = Is()
SC = LIR(m)

ans = [INF]*n
for s, c in SC:
    s -= 1
    if ans[s] == INF:
        ans[s] = c
    elif ans[s] == c:
        continue
    else:
        print("-1")
        exit()

for i in range(len(ans)):
    if i == 0 and ans[0] == INF:
        ans[0] = 1
    elif ans[i] == INF:
        ans[i] = 0

if sum(ans) == 0:
    print("-1")
    exit()

print("".join(map(str, ans)))
