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<iostream>
#include<string>
#include<vector>
using namespace std;
int main()
{
    int n,m;
    cin>>n>>m;
    vector<int> data(n);
    for(int i=0;i<m;i++)
    {
        int a,b;
        cin>>a>>b;
        if((a==1&&b==0)&&n!=1)
        {
            cout<<"-1";
            return 0;
        }
        if(data[a-1]==0||data[a-1]==b) data[a-1]=b;
        else
        {
            cout<<"-1";
            return 0;
        }
    }
    if(data[0]==0&&n!=1) data[0]=1;
    for(int i=0;i<n;i++)
        cout<<data[i];
}