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;

char num[3 + 2];

int main() {
	int N, M;
	cin >> N >> M;
	for(int i = 0; i < M; i++) {
		int s;
		char c;
		cin >> s >> c;
		--s;
		if(!(!num[s] || num[s] == c)) {
			cout << -1 << '\n';
			return 0;
		}
		num[s] = c;
	}
	for(int i = 1; i < N; i++)
		if(!num[i])
			num[i] = '0';
	if(!num[0])
		num[0] = '0' + (N != 1);
	if(num[0] == '0' && N != 1) {
		cout << -1 << '\n';
		return 0;
	}
	cout << num << '\n';
}
