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 main(){
	int n, m;
	cin >> n >> m;

	string ans(n,'a');
	for(int i=0; i<m; ++i){
		int s; 
		char c;
		cin >> s >> c;
		--s;

		if((n!=1 && s==0 && c=='0') || (ans[s]!='a' && ans[s]!=c)){
			ans="-1";
			goto OUT;
		}
		ans[s]=c;
	}
	if(ans[0]=='a'){
		if(n==1) ans="0";
		else ans[0]='1';
	}

	for(int i=1; i<n; ++i){
		if(ans[i]=='a') ans[i]='0';
	}

OUT:	cout << ans << endl;
}