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 i,j,n,m,c,d,a,b,e,k;
map<int,int> ans;
int main(){
  for(cin>>n>>m;i<m;i++){
    cin>>b>>c;
    if(b>n)return cout<<-1,0;
    if(n!=1&&b==1&&c==0)return cout<<-1,0;
    if(ans[b]==0||ans[b]==c)ans[b]=c;
    else return cout<<-1, 0;
  }
  if(n==3){
    if(ans[1]==0)ans[1]=1;
    cout<<ans[1]*100+ans[2]*10+ans[3];
  }else if(n==2){
    if(ans[1]==0)ans[1]=1;
    cout<<ans[1]*10+ans[2];
  }else{
    cout<<ans[1];
  }
}