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<iostream>
#include<vector>
using namespace std;
int main() {
  int N,M;
  cin >> N >> M;
  vector<int> A(N,-1);
  int i,s,c;
  bool F = true;
  for(i=0;i<M;i++) {
    cin >> s >> c;
    if(A[s-1] < 0 || A[s-1] == c)A[s-1] = c;
    else F = false;
  }
  if(N != 1 && A[0] == 0)F = false;
  if(N == 1 && A[0] == -1)A[0] = 0;
  if(!F)cout << -1 << endl;
  else {
    cout << (A[0]==-1?1:A[0]);
    for(i=1;i<N;i++)cout << (A[i]==-1?0:A[i]);
    cout << endl;
  }
}