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;
const int N=6;
int n,m,s[N],c[N]; 
int main()
{
    cin>>n>>m;
    for(int i=1;i<=m;i++)cin>>s[i]>>c[i];
    for(int i=0;i<1000;i++){
        string t=to_string(i);
        if(t.size()==n){
            int j;for(j=1;j<=m;j++)if(t[s[j]-1]!=c[j]+'0')break;
            if(j==m+1){cout<<i<<endl;return 0;}
        }
    }
    return cout<<-1,0;
}
