import sys
from io import StringIO
import unittest

from collections import Counter

def resolve():
    n, m = map(int, input().split())
    sc = [list(map(int, input().split())) for _ in range(m)]
    end_flag = False

    if max([s for s, c in sc]) > n:
        end_flag = True

    if (n == 2 and [2, 0] in sc) or (n == 3 and [1, 0] in sc):
        end_flag = True

    for i in range(len(sc) - 1):
        if sum([1 for s, c in sc[i+1:] if s == sc[i][0] and c != sc[i][1]]) >= 1:
            end_flag = True
            break

    ans = [0] * n

    for s, c in sc:
        ans[s - 1] = c

    if ans[0] == 0:
        ans[0] = 1
    """
    n で桁数決め
    以下の通りならアウト
    - max_sがnより大きい
    - s, cの組み合わせが一致しない、sが複数出てくる
    - n == 2 or 3で頭が0
    
    それ以外の場合
    
        
    """

    if end_flag:
        print(-1)
    else:
        print(int(''.join(map(str, ans))))

class TestClass(unittest.TestCase):
    def assertIO(self, input, output):
        stdout, stdin = sys.stdout, sys.stdin
        sys.stdout, sys.stdin = StringIO(), StringIO(input)
        resolve()
        sys.stdout.seek(0)
        out = sys.stdout.read()[:-1]
        sys.stdout, sys.stdin = stdout, stdin
        self.assertEqual(out, output)
    def test_入力例_1(self):
        input = """3 3
1 7
3 2
1 7"""
        output = """702"""
        self.assertIO(input, output)
    def test_入力例_2(self):
        input = """3 2
2 1
2 3"""
        output = """-1"""
        self.assertIO(input, output)
    def test_入力例_3(self):
        input = """3 1
1 0"""
        output = """-1"""
        self.assertIO(input, output)

if __name__ == "__main__":
    # unittest.main()
    resolve()