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>
#include<vector>
using namespace std;

int main(){
  int N,M;
  bool s=false;
  cin>>N>>M;
  vector<int> a={1,0,0};
  vector<bool> b(3,false);
  for(int i=0;i<M;i++){
    int A,B;
    cin>>A>>B;
    if(!b[A-1]){a[A-1]=B;b[A-1]=true;}
    if(b[A-1]&&a[A-1]!=B){cout<<-1;s=true;break;}
    if(N!=1&&a[0]==0){cout<<-1;s=true;break;}
  }
  if(!s&&N==3){cout<<a[0]<<a[1]<<a[2];}
  else if(!s&&N==2){cout<<a[0]<<a[1];}
  else if(!s&&N==1&&M==0){cout<<0;}
  else if(!s&&N==1){cout<<a[0];}
}