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;


long long N, M;
long long S[10];
char C[10];

int main(){
	cin >> N >> M;

	for(long long i = 0; i < M; i++) {
		cin >> S[i] >> C[i];
		S[i]--;
	}

	for(int i = 0; i < pow(10, N); i++) {
		string s = to_string(i);
		//cout << s << endl;
		if(s.size() != N) 
			continue;

		bool ok= true;
		for(long long j = 0; j < M; j++) {
			if(s[S[j]] != C[j]) {
				ok = false;
			}
		}
		if(ok) {
			cout << s << endl;
			return 0;
		}
	}
	cout << -1 << endl;
}
