n, m = map(int, input().split())
s = []
c = []
for i in range(m):
    rets, retc = map(int, input().split())
    s.append(rets)
    c.append(retc)

ans = ["-1"] * n
check = True

for i in range(m):
    if ans[s[i] - 1] == str(c[i]) or ans[s[i] - 1] == "-1":
        ans[s[i] - 1] = str(c[i])
    else:
        check = False
if (n == 1 and ans.count("-1") == n) or (n != 1 and ans[0] == "0"):
    check = False
for i in range(n):
    if ans[i] == "-1":
        if i == 0:
            ans[i] = "1"
        else:
            ans[i] = "0"
if check:
    print(''.join(ans))
else:
    print(-1)
