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>
using namespace std;
int s[3],n,m,a,b;
int main(void){
    cin>>n>>m;
    for(int i=0;i<3;i++)s[i]=-1;
    for(int i=0;i<m;i++){
        cin>>a>>b;
        a--;
        if(s[a]!=-1&&s[a]!=b){cout<<-1<<endl;return 0;}
        s[a]=b;
    }
    if(n!=1&&s[0]==0){cout<<-1<<endl;return 0;}
    if(s[0]==-1){
        if(n==1)s[0]=0;
        else s[0]=1;
    }
    if(s[1]==-1)s[1]=0;
    if(s[2]==-1)s[2]=0;
    for(int i=0;i<n;i++){
        cout<<s[i];
    }
    cout<<endl;
}
