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;
#define rep(i, n) for(int i = 0; i < (int)(n); i++)
 
int main(void){ 
  int n,m;
  int i,j;
  int ans=0;
  cin>>n>>m;
  vector<int> a(n,0);
  vector<int> c(m,0);
  vector<int> s(m,0);
  if(n!=1)a.at(0)=1;
  rep(i,m){
    cin>>s.at(i)>>c.at(i);
    a.at(s.at(i)-1)=c.at(i);
  }
  rep(i,m){
    if(a.at(s.at(i)-1)!=c.at(i)){ans=-1;}
    if(s.at(i)==1&&c.at(i)==0&&n!=1){ans=-1;}
  }  
  if(ans!=-1)
    rep(i,n)cout<<a.at(i);
  else{cout<<ans;}
  
}