def main():
    n , m = map(int, input().split())
    con = list(set([tuple(map(int, input().split())) for i in range(m)]))
    if (len(con) > n) or (n != 1 and con[0] == (1,0)):
        print(-1)
        return
    ans = 10**(n-1)
    tmp = -1
    for s,c in con:
        if (s == tmp):
            print(-1)
            return
        else:
            tmp = s
        if (s==1):
            ans += (c-1)*10**(n-1)
        else:
            ans += c*10**(n-s)
    print(ans)
main()   