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().split())

ans = ""
for i in range(N):
     ans = ans + "a"

ans = list(ans)
flag = True

for i in range(M):
     s, c = map(int, raw_input().split())
     if ans[s-1] == "a":
          ans[s-1] = c
     elif ans[s-1] != c:
          flag = False

if N == 1:
     if ans[0] == "a" or ans[0] == 0:
          print "0"
          exit()


new = ""
if ans[0] == "a":
     ans[0] = 1
for i in range(N):
     if ans[i] == "a":
          new = new+"0"
     else:
          new = new + str(ans[i])

if new[0] == "0":
     flag = False

if N == 1:
     if new[0] == 0:
          flag = True

if flag == True:
     print new
else:
     print "-1"
