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>
using namespace std;

int n,m,s[9],c[9],d[9],ans;
bool ok[9];

int main()
{
	cin >> n >> m;
	for(int i = 1;i<=m;i++)
	{
		cin >> s[i] >> c[i];
		if(ok[s[i]] and c[i]!=d[s[i]])
		{
			cout << -1;
			return 0;
		}
		if(s[i]==1 and c[i]==0 and n!=1)
		{
			cout << -1;
			return 0;
		}
		d[s[i]] = c[i];
		ok[s[i]] = 1;
	}
	if(ok[1]==0 and n!=1)d[1] = 1;
	if(n==1)cout << d[1];
	if(n==2)cout << d[2]+d[1]*10;
	if(n==3)cout << d[3]+d[2]*10+d[1]*100;
	return 0;
}