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

        if(n!=1&&s==1&&c==0){
            cout << -1 <<endl;
            return 0;
        }
        
        ans[s] =c;
    }

    
    
    if(ans[1]==0 && n!=1){
        ans[1] =1;
    }

    for(int h=1;h<n+1;h++){
        cout << ans[h];
    }
}