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