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 t;
	for(int i=0; i<n; i++) t+='0';
	map<int,int> a;
	for(int i=1; i<=3; i++) a[i]=-1;
	
	bool flg=1;
	for(int i=0; i<m; i++){
		int s,c;
		cin >> s >> c;
		if(n!=1 && s==1 && c==0) flg=0;
		if(a.at(s)!=-1 && a.at(s)!=c) flg=0;
		a.at(s)=c;
		t.at(s-1)=(char) (c+'0');
	}
	if(n==3 && a.at(1)==-1) t.at(0)='1';
	if(n==2 && a.at(1)==-1) t.at(0)='1';
	if(!flg) cout << "-1" << endl;
	else cout << stoi(t) << endl;
	
}