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
import sys

def main():
    line = sys.stdin.readline().rstrip('\n').split()
    N , M = int(line[0]), int(line[1])
    ans = 0

    conditions = {}
    for i in range(M):
        line = sys.stdin.readline().rstrip('\n').split()
        if int(line[0]) not in conditions.keys():
            conditions[int(line[0])] = int(line[1])
        else:
            if conditions[int(line[0])] != int(line[1]):
                print(-1)
                return

    if ((1 in conditions.keys()) and conditions[1]==0 and N!=1):
       print(-1)
       return

    if (1 in conditions.keys()):
        ans += conditions[1]*(10**(N-1))
    else:
        if (N!=1):
            ans += 10**(N-1)

    if (2 in conditions.keys()):
        ans += conditions[2]*(10**(N-2))

    if (3 in conditions.keys()):
        ans += conditions[3]

    print(ans)

main()
