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 n, m;
int a[11];

int main() {
	scanf("%d%d", &n, &m);
	memset(a, -1, sizeof a);
	
	bool chk = true;
	for(int i=0;i<m;i++) {
		int x, y;
		scanf("%d%d", &x, &y);
		if(a[x]<0) a[x]=y;
		else
		if(a[x]!=y) chk = false;
	}
	if(n>1&&a[1]==0) chk = false;
	
	if(!chk) puts("-1");
	else {
		for(int i=1;i<=n;i++)
			if(a[i]<0) a[i]=((i==1&&n>1)?1:0);
		for(int i=1;i<=n;i++)
			printf("%d", a[i]);
		puts("");
	}
	
	return 0;
}