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;
    cin >> n >> m;
    string r(n, 'a');
    for(int i = 0; i < m; i++) {
        int s, c;
        cin >> s >> c;
        if(n != 1 && s == 1 && !c || r[s - 1] != 'a' && r[s - 1] != c + '0') {
            cout << -1 << endl;
            return 0;
        }
        r[s - 1] = c + '0';
    }
    for(int i = 0; i < n; i++)
        if(r[i] == 'a')
            r[i] = n > 1 ? !i + '0' : '0';
    cout << r << endl;
    return 0;
}
