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
input = raw_input

n, m = map(int, input().split(" "))
pairs = set( [tuple(map(int, input().split(" "))) for _ in range(m)] )
#pairs = sorted(tmp , key=lambda x: x[0])

values = [None] * (n+1)

flag = True
for s, c in pairs:
    if s == 1 and c == 0 and n != 1:
        flag = False
        break

    if values[s] is not None:
        flag = False
        break

    values[s] = c

if flag:
    out = 0
    for i in range(1, n+1):
        value = values[i]
        if value is None:
            if i == 1 and n != 1:
                value = 1
            else:
                value = 0

        j = n - i + 1
        out += value * (10 ** (j-1)) 

else:
    out = -1

print(out)