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;
typedef long long ll;
ll read(){
	int a=0,b=getchar();
	while(!isdigit(b))b=getchar();
	while(isdigit(b))a=a*10+b-'0',b=getchar();
	return a;
}
int n,m,a[5];
int main(){
	memset(a,-1,sizeof(a));
	n=read(),m=read();
	while(m--){
		int x=read(),y=read();
		if(a[x]!=-1 and a[x]!=y)return puts("-1"),0;
		a[x]=y;
	}
	if(n!=1 and a[1]==0)return puts("-1"),0;
	for(int i=1;i<=n;i++){
		if(a[i]!=-1)cout << a[i];
		else if(i!=1 or n==1)cout << 0;
		else cout << 1;
	}
	return 0;
}