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<iostream>
using namespace std;
int main(){
  int n,m;
  cin>>n>>m;
  int a[n];
  for(int i=0;i<n;i++)a[i]=-1;
  for(int i=0;i<m;i++){
    int s;
    cin>>s;
    s--;
    if(a[s]==-1)cin>>a[s];
    else{
      int t;
      cin>>t;
      if(t!=a[s]){
        cout<<-1<<endl;
        return 0;
      }
    }
  }
  if(a[0]==0){
    if(n>1){
      cout<<-1<<endl;
      return 0;
    }
  }if(a[0]==-1)a[0]=n>1?1:0;
  for(int i=0;i<n;i++)cout<<(a[i]==-1?0:a[i]);
  endl(cout);
}