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 main() {
  int n,m;
  bool flag = true;
  cin >> n >> m;
  vector<int> a(n,0);
  for(int i = 0; i < m; i++) {
    int s,c;
    cin >> s >> c;
    if(a[s-1] != 0 && a[s-1] != c) {flag = false; break;}
    if(s == 1 && c == 0 && n != 1) {
      cout << "-1" << endl;
      return 0;
    }
    a[s-1] = c;
  }
  if(a[0] == 0 && n != 1) a[0] = 1;
  if(flag) {
    for(int i = 0; i < n; i++) cout << a[i];
    cout << endl;
  }
  else cout << "-1" << endl;
  return 0;
}