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,s[5],c[5];
string S;

int main(){
	cin>>N>>M;
	S=string(N,0);
	for(int i=0;i<M;i++){
		cin>>s[i]>>c[i];
		s[i]--;
		if(N!=1&&s[i]==0&&c[i]==0){
			cout<<-1<<endl;
			return 0;
		}
		if(S[s[i]]==0||S[s[i]]=='0'+c[i]){
			S[s[i]]='0'+c[i];
		}
		else{
			cout<<-1<<endl;
			return 0;
		}
	}
	for(int i=0;i<N;i++){
		if(S[i]==0){
			if(i==0&&N!=1)cout<<1;
			else cout<<0;
		}
		else cout<<S[i];
	}
	cout<<endl;
}
