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 n,m;
int s,c;
int a[10];
bool ans;
int main() {
	cin>>n>>m;
	if(n==1&&m==0) {
		cout<<0;
		return 0;
	}
	for(int i=1;i<=5;i++) a[i]=-1;
	for(int i=1;i<=m;i++) {
		cin>>s>>c;
		if(s==1&&c==0&&n!=1) ans=1;
		else if(a[s]==-1) a[s]=c;
		else if(a[s]!=c) ans=1;
	}
	if(ans) {
		cout<<-1;
		return 0;
	}
	if(a[1]==-1) cout<<1;
	else cout<<a[1];
	for(int i=2;i<=n;i++) {
		if(a[i]==-1) cout<<0;
		else cout<<a[i];
	} 
	return 0;
}