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 <cstdio>

int n, m;
int a[5];

int main() {
    scanf("%d%d", &n, &m);
    for (int i = 1; i <= n; ++i) a[i] = -1;
    for (int i = 1, x, y; i <= m; ++i) {
        scanf("%d%d", &x, &y);
        if (~a[x] && a[x] ^ y) return puts("-1"), 0;
        a[x] = y;
    }
    if (n == 1) return printf("%d\n", ~a[1] ? a[1] : 0), 0;
    if (!a[1]) return puts("-1"), 0;
    for (int i = 1; i <= n; ++i) printf("%d", ~a[i] ? a[i] : (i == 1 ? 1 : 0));
    return 0;
}
