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;
  int num[3];
  for(int i=0;i<3;i++) num[i]=-1;
  cin>>n>>m;
  bool f=true;
  int s,c;
  for(int i=0;i<m;i++){
    cin>>s>>c;
    if(num[s-1]!=-1 && c!=num[s-1]){
      f=false;
    }
    num[s-1]=c;
  }
  if(num[0]==-1&&n>1) num[0]=1;
  if(num[0]==-1&&n==1) num[0]=0;
  if(num[0]==0 &&n>1) f=false;
  for(int i=1;i<3;i++){
    if(num[i]==-1) num[i]=0;
  }
  if(f==false) cout<<-1<<endl;
  else{
    for(int i=0;i<n;i++)
      cout<<num[i];
    cout<<endl;
  }
}
