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
#!/usr/bin/env python

from sys import stdin, stderr

INF = 100000
def solve(N, rules):
   res = INF
   for num in xrange(10**N):
      snum = str(num)
      if len(snum) != N:
         continue
      ok = True
      for s, c in rules:
         if ord(snum[s-1])-ord('0') != c:
            ok = False
            break
      if ok:
         res = min(res, num)
   return res if res < INF else -1

def main():
   N, M = map(int, stdin.readline().split())
   rules = []
   for i in xrange(M):
      rules.append( map(int, stdin.readline().split()) )

   res = solve(N, rules)
   print(res)

   return 0

if __name__ == '__main__': main()
