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()
{
ios_base::sync_with_stdio(false);
cout.tie(0);
cin.tie(NULL);
int n,m; cin>>n>>m;
int a[n];
for(int i=0;i<n;i++)
a[i]=10;
if(n==1&&m==0)
{
	cout<<0; return 0;
}
while(m--)
{
	int s,c;
	cin>>s>>c;
	if(a[s-1]!=10&&a[s-1]!=c)
	{
		cout<<-1; return 0;
	}
	a[s-1]=c;
}
if(a[0]==10)
cout<<1;
else if(a[0]==0&&n>=2)
{
		cout<<-1; return 0;
}
else
cout<<a[0];
for(int i=1;i<n;i++)
{
	if(a[i]==10)
	{
		a[i]=0;
	}
	cout<<a[i];
}
}
