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>
#include <cstdio>
using namespace std;

int n, m, s, c, d[5];
int main() {
	int i;
	cin >> n >> m;
	for(i=1; i<=n; i++) d[i] = -1;
	while(m--) {
		cin >> s >> c;
		if(d[s]>-1 && d[s]!=c) return puts("-1")*0;
		d[s] = c;
	}
	if(n>1 && d[1]==0) return puts("-1")*0;
	if(d[1]==-1) {
		if(n==1) d[1] = 0;
		else d[1] = 1;
	}
	for(i=1; i<=n; i++) {
		if(d[i]>-1) cout << d[i];
		else cout << 0;
	}
	return 0;
}