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(void){
  int N,M;
  cin>>N>>M;
  vector<int> s(M);
  vector<int> c(M);
  for(int i=0;i<M;i++){
    cin>>s[i]>>c[i];
  }
  for(int i=0;i<1000;i++){
    string x=to_string(i);
    bool flag=false;
    if(x.size()==N){
      flag=true;
      for(int j=0;j<M;j++){
        if(x[s[j]-1]!=c[j]+'0') flag=false;
      }
    }
    if(flag){
      cout<<i<<endl;
      return 0;
    }
  }
  cout<<-1<<endl;
  return 0;
}
