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>
#define rep(i,n) for (int i = 0; i < (n); i++)
using namespace std;
using ll = long long;

int main(){
  int n,m; cin >>n >>m;
  int s[6], c[6];
  rep(i,m) cin >>s[i] >>c[i];
  rep(i,1000){
    string str = to_string(i);
    if(str.size()==n){
      int cnt = 0;
      rep(j,m){
        if(str[s[j]-1]!=c[j]+'0') break;
        else cnt++;
      }
      if(cnt==m){
        cout << i << endl;
        return 0;
      }
    }
  }
  cout << -1 << endl;
  return 0; 
}