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 main(){
  int n,m,x=0;
  int a[3]={0,0,0};
  cin>>n>>m;
  int s[m],c[m];
  for(int i=0;i<m;i++){
    cin>>s[i]>>c[i];
    if((a[s[i]-1]!=0&&a[s[i]-1]!=c[i])||(n!=1&&s[i]==1&&c[i]==0)){
      cout<<"-1";
      x=1;
      break;
    }else{
      a[s[i]-1]=c[i];
    }
  }
  if(a[0]==0&&n!=1)a[0]=1;
  if(x==0){
    if(n==1){
      cout<<a[0];
    }
    if(n==2){
      cout<<a[0]<<a[1];
    }
    if(n==3){
    cout<<a[0]<<a[1]<<a[2];
    }
  }
  
  return 0;
}