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 ans[10];

int main(){
	memset(ans,-1,sizeof(ans));
	scanf("%d%d",&n,&m);
	while(m--){
		int s,c;
		scanf("%d%d",&s,&c);
		if(ans[s] == -1){
			ans[s] = c;
		} else if(ans[s] != c){
			printf("-1\n");
			return 0;
		}
	}
	if(ans[1] == 0 && n > 1){
		printf("-1\n");
		return 0;
	}
	if(ans[1] == -1) {
		if(n == 1) ans[1] = 0;
		else ans[1] = 1;
	}
	for(int i=1;i<=n;i++){
		if(ans[i] == -1) ans[i] = 0;
		printf("%d",ans[i]);
	}
	printf("\n");
	return 0;
}
