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,c,n) for(int i=c;i<n;i++)
 
int main(void) {
  int n,m;
  cin>>n>>m;
  
  string str;
  if(n==1){str="0";}
  if(n==2){str="10";}
  if(n==3){str="100";}
  
  vector<int> a(n,-1);
  bool empty=0;
  rep(i,0,m){
    int s,c;
    cin>>s>>c;
    if(s==1&&n>1&&c==0){empty=1;break;}
    if(a[s-1]==-1||a[s-1]==c){
      a[s-1]=max(a[s-1],c);
      str[s-1]=c+'0';
    }
    else{empty=1;break;}
  }

  if(empty==1){cout<<-1<<endl;}
  else{cout<<str<<endl;}

  return 0;
}
