n,m = map(int,input().split())
t = [0 for i in range(n)]
e = [True for i in range(n)]
b = ""
a = False
for i in range(m):
    s,c = map(int,input().split())
    if e[s-1]:
        if s == 1 and c == 0:
            a = True
        else:
            t[s-1] = c
            e[s-1] = False
    else:
        if t[s-1] != c:
            a = True
for i in range(n):
    b += str(t[i])
if a:
    print(-1)
elif n > 1 and b[0] == '0':
    print(str(1)+b[1:3])
else:
    print(b)