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(void){
  int n,m;
  cin>>n>>m;
  vector<bool> tf(n);
  vector<int> num(n);
  for(int i=0;i<m;i++){
    int s,c;
    cin>>s>>c;
    if(tf[s-1] && num[s-1]!=c){
      cout<<-1<<endl;
      return 0;
    }else if(s==1 && c==0 && n!=1){
      cout<<-1<<endl;
      return 0;
    }else{
      tf[s-1]=true;
      num[s-1]=c;
    }
  }
  if(num[0]==0 && n!=1){
    num[0]=1;
  }
  for(int i=0;i<n;i++){
    cout<<num[i];
  }
  return 0;
}