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
#include <bits/stdc++.h>

using namespace std;

int arr[5];

int main()
{
  int n,m;
  cin >> n >> m;
  
  for(int i=0;i<5;i++)arr[i]=-1;
  
  while(m--)
  {
    int i,x;
    cin >> i >> x;
    if(arr[i]!=x and arr[i]!=-1)
    {
      cout << -1;
      return 0;
    }
    arr[i]=x;
  }
  
  if(arr[1]==-1 and n>1)arr[1]=1;
  else if(arr[1]==-1 and n==1)arr[1]=0;
  for(int i=2;i<=n;i++)if(arr[i]==-1)arr[i]=0;
  
  if(n>1 and arr[1]==0)
  {
    cout << -1;
    return 0;
  }
  
  for(int i=1;i<=n;i++)cout << arr[i];
  
}
