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 a[3];

int main(){
    int n,m; cin >> n >> m;
    bool na=false;
    for(int i=0;i<m;i++){
        int s,c; cin >> s >> c; s--;
        if(n!=1 && s==0 && c==0) na=true;
        if(a[s]!=0 && a[s]!=c) na=true;
        else a[s]=c;
    }
    if(n!=1 && a[0]==0) a[0]=1;
    if(na){
        cout << -1;
    }else{
        for(int i=0;i<n;i++){
            cout << a[i];
        }
    }
    cout << endl;
}