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;
  int s[M];
  char c[M];
  for(int i=0; i<M; i++) cin >> s[i] >> c[i]; 
  int ans=-1;
  for(int i=(N==1 ? 0 : pow(10,N-1)); i<pow(10,N); i++){
    string S = std::to_string(i);
    int cnt=0;
    for(int j=0; j<M; j++){
      if(S.at(s[j]-1)==c[j]) cnt++;
    }
    if(cnt==M){
      ans=i;
      break;
    }
  }
  cout << ans << endl;
}