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
def main():
    n, m = map(int, raw_input().split())
    aa = [None] * n
    for _ in xrange(m):
        s, c = raw_input().split()
        s = int(s) - 1
        if aa[s] is not None and aa[s] != c:
            print '-1'
            return
        aa[s] = c
    if n == 1:
        if aa[0] is None:
            print 0
        else:
            print aa[0]
        return
    if aa[0] is None:
        aa[0] = '1'
    for i, a in enumerate(aa):
        if a is None:
            aa[i] = '0'
    if aa[0] == '0':
        print -1
    else:
        print ''.join(aa)

main()
