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;

const int N=5;

int n,m,s,c,dp[N];
bool ok=true;

int main()
{
	cin>>n>>m;
	for(int i=1;i<=n;i++) dp[i]=-1;
	while(m--)
	{
		cin>>s>>c;
		if(dp[s]==-1) dp[s]=c;
		else if(dp[s]!=c) ok=false;
	}
	if(dp[1]!=-1)
	{
		if(dp[1]==0 and n>1) ok=false;
	}
	if(dp[1]==-1)
	{
		if(n==1) dp[1]=0;
		else dp[1]=1;
	}
	for(int i=1;i<=n;i++)
		if(dp[i]==-1) dp[i]=0;

	if(ok)
	{
		for(int i=1;i<=n;i++) cout<<dp[i];
	}
	else cout<<"-1";
}