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>
#define rep(i,n) for (int i=0; i<(n); i++)
using namespace std;

int main() {
  int n, m;
  cin >> n >> m;
  vector<int> s(m);
  vector<char> c(m);
  rep(i,m) cin >> s.at(i) >> c.at(i);
  
  int st = 0;
  if (n >= 2) st = pow(10,n-1);
  int ed = pow(10,n);
  int ans = -1;
  for (int i = st; i < ed; i++) {
    string x = to_string(i);
    bool t = true;
    rep(j,m) {
      if (x.at(s.at(j)-1) != c.at(j)) t = false;
    }
    if (t) {
      ans = i;
      break;
    }
  }
  cout << ans << endl;
}