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<map>
using namespace std;
int a[4];
map<int,int>mp;
int main()
{
	string str;
	int n,m,s,c,maxn=-1,minn=4;
	cin>>n>>m;
	for(int i=1;i<=m;i++)
	{
		scanf("%d%d",&s,&c);
		mp[s]++;
		maxn=max(maxn,s);
		minn=min(minn,s);
		if(mp[s]>1&&c!=a[s])
		{
			printf("-1\n");
			return 0;
		}
		a[s]=c;		
	}
	if(mp[1]==0&&n!=1)
	{
		a[1]=1;
	} 
	if(mp[1]>0&&a[1]==0&&n!=1)
	{
		printf("-1\n");
		return 0;
	}
	for(int i=1;i<=n;i++)printf("%d",a[i]);
	printf("\n");
	return 0;
}