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 A(n, '0');
    vector<bool> B(n);
    for (int i = 0; i < m; i++){
        int s, c;
        cin >> s >> c;
        s--;
        if ((B[s] and A[s] - '0' != c) or (n != 1 and s == 0 and c == 0)){
            puts("-1");
            return 0;
        }
        A[s] = c + '0';
        B[s] = true;
    }
    if (A[0] == '0' and n != 1)
        A[0] = '1';
    cout << A << endl;
}