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;
  cin>>N>>M;
  vector<int>data(N,-1);
  for(int i=0;i<M;i++){
    int s,a;
    cin>>s>>a;
    s--;
    if(data[s]==-1){
      data[s]=a;
    }else if(data[s]!=a){
      cout<<-1<<endl;
      return 0;
    }
  }
  for(int i=0;i<N;i++){
    if(N!=1&&(data[0]==0)){
      cout<<-1<<endl;
      return 0;
    }
    if(N!=1&&data[0]==-1)data[0]=1;
    else if(data[i]==-1)data[i]=0;
    cout<<data[i];
  }cout<<endl;
}