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 q[5][2];
  for(int i=0; i<M; i++){
    cin >> q[i][0] >> q[i][1];
  }
  
  int len=1;
  while(N--) len*=10;
  
  for(int i=len/10-(len/10==1?1:0); i<len; i++){
    string str=to_string(i);
    bool f=true;
    for(int j=0; j<M; j++){
      if(str[q[j][0]-1]-'0'!=q[j][1]) f=false;
    }
    if(f==true){
      cout << str << endl;
      return 0;
    }
  }
  cout << -1 << endl;
}