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 <cstdio>
#define F(i,x,y) for(int i=x;i<=y;++i)
using namespace std;
int a[5]={10,10,10,10,10},n,m,s,c;
bool flag=false;
int main(){
	scanf("%d%d",&n,&m);
	F(i,1,m){
		scanf("%d%d",&s,&c);
		if(s==1&&c==0&&n>1)flag=true;
		if(s>3)flag=true;
		if(a[s]!=10&&a[s]!=c)flag=true;
		a[s]=c;
	}
	if(flag){
		printf("-1\n");
		return 0;
	}
	F(i,1,n)if(a[i]==10)a[i]=0;
	if(a[1]==0&&n!=1)a[1]=1;
	F(i,1,n)printf("%d",a[i]);
	printf("\n");
	return 0;
}
