#!/usr/bin/python
# -*- coding: utf-8 -*-

# 入力はstringで入る．
# intにしたければ int(input())
# floatで受け取ると 1.0 になる．

import numpy as np

# 入力
N,M = map(int,input().split())

SC = [list(map(int,input().split())) for l in range(M)]

L = np.zeros((10,N,))
counter = 0

if [1,0] in SC:
    print(-1)
else:
    for i in range(M):
        L[SC[i][1],SC[i][0]-1] = SC[i][1]

    for k in range(N-1):
        if np.count_nonzero(L[:,N-1-k] > 0) > 1:
            counter = -1
            
    if np.count_nonzero(L[:,0] > 0) > 1:
        counter = -1
    elif np.count_nonzero(L[:,0] > 0) == 0:
        L[1,0] = 1

    if counter == -1:
        print(-1)
    else:
        print("".join([str(int(k)) for k in list(np.sum(L,axis=0))]))


