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 main()
{
   int n,m;
   cin>>n>>m;
   if (n==1 && m==0)
   {
       cout<<0;
       return 0;
   }
   vector<int>a(n,-1);
   while(m--)
   {
       int s,c;
       cin>>s>>c;s--;
       if (a[s]!=-1 && a[s]!=c || (s==0 && c==0 && n!=1))
       {
           cout<<-1;
           return 0;
       }
       a[s]=c;
   }
   if (a[0]==-1)
    a[0]=1;
   for (int i=0;i<n;i++)
    if (a[i]!=-1)
         cout<<a[i];
   else
    cout<<0;
    return 0;
}