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;
bool used[10001];
int n,a,b,m;
string ans;
int main()
{
	scanf("%d%d",&n,&m);
	for(int i=1;i<=n;i++)ans+='0';
	ans[0]='1';
	while(m--)
	{
		scanf("%d%d",&a,&b);
		--a;
		if(used[a]&&b!=ans[a]-48)
		{
			puts("-1");
			return 0;
		}
		used[a]=1;
		ans[a]=b+48;
	}
	if(n==1&&used[0]==0)
	{
		puts("0");
		return 0;
	 } 
	if(ans[0]=='0'&&used[0]==1)
	{
		if(n!=1)puts("-1");
		else puts("0");
		return 0;
	}
	cout<<ans;
	return 0;
}