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;

template<typename T>
void fin(T a){
  cout<<a<<endl;
  exit(0);
}

signed main(){
  int n,m;cin>>n>>m;
  if(n==1){
    int ans=-1;
    while(m--){
      int s,c;cin>>s>>c;
      if(~ans&&ans!=c)fin(-1);
      ans=c;
    }
    fin(max(ans,0));
  }
  vector<int> v(n,-1);
  while(m--){
    int s,c;cin>>s>>c;
    if(s==1&&c==0)fin(-1);
    if(~v[s-1]&&v[s-1]!=c)fin(-1);
    v[s-1]=c;
  }
  if(!~v[0])v[0]=1;
  for(int i=0;i<n;i++){
    cout<<(~v[i]?v[i]:0);
  }
  cout<<endl;
}
