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<n;i++)


int main()
{
   int n,m;
  cin>>n>>m;
  
  vector<int>s(m);
  char c[m];
  
  rep(i,m)
  {
     cin>>s[i]>>c[i];
  }

for(int x=0;x<1000;x++)
{
   string a = to_string(x);
   if(a.size()!=n) continue;
  
   bool ok = true;
   for(int i=0;i<m;i++)
   {
       if(a[s.at(i)-1] != c[i]) ok = false;
 
   }
  if(ok)
  {  
    cout<<x<<endl;
    return 0;
  }
}

cout<<-1<<endl;
  
  return 0;

}
