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;
  int i;
  int t,u;
  
  cin >> N >> M;
  vector<int> num(N);

  for(i=0;i<M;++i){
    cin >> t >> u;
    if(t == 1 && u == 0 && N != 1){
      cout << -1 << endl;
      return 0;
    }
    if(num.at(t-1) == 0 || num.at(t-1) == u){
      num.at(t-1) = u;
    }else{
      cout << -1 << endl;
      return 0;
    }
  }

  if(num.at(0) == 0 && N != 1){
    num.at(0) = 1;
  }
  for(i=0;i<N;++i){
    cout << num.at(i);
  }
  cout << endl;
}