n,m = map(int,input().split())
s = [0] * m
c = [0] * m
a = [0] * n
for i in range(m):
    s[i],c[i] = map(int,input().split())
#
ans = 0
for j in range(m):
    if s[j] == 1 and c[j] == 0:
        ans = -1
    else:
        if a[s[j] - 1] == 0:
            a[s[j] - 1] = c[j]
        else:
            if a[s[j] - 1] != c[j]:
                ans = -1
                break
#

if m == 0:
    ans = 10 ** (n - 1)
elif ans != -1:
    if a[0] == 0:
        ans = 10 **(n - 1)
        for i in range(n):
            ans += a[i] * 10 **(n - i - 1)
    else:
        for i in range(n):
            ans += a[i] * 10 **(n - i - 1)

print(ans)
