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 main(){
    int n, m;
    cin >> n >> m;
    int t[m], c[m];
    for(int i = 0; i < m; i++)  cin >> t[i] >> c[i];
    int ret = -1;
    for(int i = 0; i < 1000; i++){
        string s = to_string(i);
        if(s.length() != n) continue;
        bool val = true;
        for(int j = 0; j < m; j++)  val &= s[t[j]-1]-'0'==c[j];
        if(val){
            ret = i;
            break;
        }
    }
    cout << ret << endl;
    return 0;
}