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
// C - Guess The Number
#include <bits/stdc++.h>
using namespace std;

int main(){
	int N,M; cin>>N>>M;
	string T(N,'-');
	while(M--){
		int s,c; cin>>s>>c; s--, c+='0';
		if(T[s] !='-' && T[s] != c){ puts("-1"); return 0; }
		if(N!=1 && s==0 && c=='0'){ puts("-1"); return 0; }
		T[s] = c;
	}

	while(N--)
		if(T[N]=='-')
			if(T.size()==1) T[N] = '0';
			else T[N] = N==0? '1': '0';
	cout<< stoi(T) <<endl;
}