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