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

if flag == 0:
    if ans[3-n]==0:
        ans[3-n]=1
    print(''.join(map(str, ans)))
else:
    print(-1)