N,M = map(int,input().split(" "))
ans = [-1 for _ in range(N)]
for i in range(M):
    s,c = map(int,input().split(" "))
    if ans[s-1] != -1 and ans[s-1] != c:
        print(-1)
        exit()
    else:
        ans[s-1] = c
if ans[0] == 0:
    print(-1)
    exit()  
for i in range(N):
    if ans[i] == -1:
        if i != 0:
            ans[i] = 0
        else:
            ans[i] = 1
    ans[i] = str(ans[i])
ans = ''.join(ans)
print(int(ans))