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;
using ll = long long;
using P = pair<int,int>;

int main() {
  int n, m;
  cin >> n >> m;
  int a[3]={0,0,0};
  rep(i,m) {
    int s, c;
    cin >> s >> c;
    if(n!=1&&s==1&&c==0) {
      cout << -1 << endl;
      return 0;
    }
    if(a[s-1]!=0&&a[s-1]!=c) {
      cout << -1 << endl;
      return 0;
    }
    a[s-1] = c;
  }
  if(n!=1&&a[0]==0) a[0]=1;
  rep(i,n) cout << a[i];
  cout << endl;
}
