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;
  int ans = -1;
  cin >> N >> M;
  vector<pair<int, char>> sc(M);
  for (int i = 0; i < M; ++i) {
    cin >> sc[i].first >> sc[i].second;
  }
  for (int i = pow(10, N-1)-1, ma = pow(10, N); i < ma; ++i) {
    bool flag = 1;
    string s = to_string(i);
    if (int(s.size()) != N) continue;
	for (int j = 0; j < M; ++j) {
	  if (s[sc[j].first-1] != sc[j].second) {flag = 0; break;}
    }
    if (flag) {ans = i; break;}
  }
  cout << ans << "\n";
}