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;
typedef long long ll;
#define rep(i,n) for(int i=0;i<n;i++)

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

	vector<int>a(n,-1);

	rep(i,m) {
		int s, c;
		cin >> s >> c;
		if (a[s-1]!=-1 && a[s - 1]!=c) {
			cout << -1<<endl;
			return 0;
		}
		else {
			a[s - 1] = c;
		}
	}

	if (a[0]==0 && n!=1) {
		cout << -1 << endl;
		return 0;
	}
	else if(a[0] == -1 && n != 1) {
		a[0] = 1;
	}

	rep(i,n){
		if (a[i]!=-1) {
			cout << a[i];
		}
		else {
			cout << 0;
		}
	}

	return 0;
}
