If there is an integer not less than 0 satisfying the following conditions, print the smallest such integer; otherwise, print `-1`.

* The integer has exactly N digits in base ten. (We assume 0 to be a 1-digit integer. For other integers, leading zeros are not allowed.)
* The s_i-th digit from the left is c_i. \left(i = 1, 2, \cdots, M\right)

Constraints

* All values in input are integers.
* 1 \leq N \leq 3
* 0 \leq M \leq 5
* 1 \leq s_i \leq N
* 0 \leq c_i \leq 9

Input

Input is given from Standard Input in the following format:


N M
s_1 c_1
\vdots
s_M c_M


Output

Print the answer.

Examples

Input

3 3
1 7
3 2
1 7


Output

702


Input

3 2
2 1
2 3


Output

-1


Input

3 1
1 0


Output

-1
n, m = map(int, raw_input().strip().split())

f = dict()

for i in xrange(m):
    s, c = map(int, raw_input().strip().split())
    try: f[s - 1].append(c)
    except: f[s - 1] = [c]

for key in f:
    f[key] = list(set(f[key]))
    if len(f[key]) > 1:
        print -1
        exit()

for i in xrange(1000):
    X = str(i)

    if len(X) != n:
        continue

    flag = 0
    for key in f:
        if key >= len(X):
            flag = 1
            break
        if X[key] != str(f[key][0]):
            flag = 1
            break

    if flag == 0 and len(X) == n:
        print X
        exit()

print -1
    
