import sys 
a = list(map(int,input().split()))

N = a[0]
M = a[1]

b = ['0']*N

for i in range(0,M):
    x = list(map(str,input().split()))
    if b[int(x[0])-1] != '0' and b[int(x[0])-1] != x[1]: #既に与えられたところに違う値
        print('-1')
        sys.exit()
    elif x[0] == '1' and x[1] == '0': #the first digit is  "0"
        print('-1')
        sys.exit()
    else:
        b[int(x[0])-1] = x[1]

if N != 1 and b[0] == '0':
    b[0] = '1'

ans = ''.join(b)
print(int(ans))
