p02761 AtCoder Beginner Contest 157 - Guess The Number
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
```python
N,M = map(int,input().split())
SCdash = [[int(i) for i in input().split()] for m in range(M)]
SC = [[scc[0]-1,str(scc[1])] for scc in SCdash]
SG = [(0,10),(10,100),(100,1000)]
for x in range(*SG[N-1]):
    keta = str(x)
    if all([keta[s]==c for s,c in SC]):
        print(x)
        exit()
print(-1)

```