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,f=0,i,s,c;
	
	cin>>n>>m;
	int ar[n];
	for(i=0;i<n;i++) ar[i]=-1;
	for(i=0;i<m;i++)
	{
		cin>>s>>c;
		if(f) continue;
		if((n>1 && s==1 && c==0) || (ar[s-1]!=-1 && c!=ar[s-1])) f=1;
		else ar[s-1]=c;
	}
	if(f) cout<<"-1\n";
	else 
	{
		if(n>1 && ar[0]==-1) cout<<1; else cout<<max(ar[0],0);
		for(i=1;i<n;i++) cout<<max(ar[i],0);
	}
}