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;
typedef int64_t ll;

int main() {
  int n,m,s;
  char c;
  cin >> n >> m;
  string ans="";
  for(int i=0;i<n;i++) ans.push_back('x');
  for(int i=0;i<m;i++){
    cin >> s >> c;
    if(ans[s-1]=='x' || ans[s-1]==c) ans[s-1]=c;
    else{cout << -1 << endl; return 0;}
  }
  if(ans[0]=='x') ans[0]=(n==1?'0':'1');
  if(n>1 && ans[0]=='0'){cout << -1 << endl; return 0;}
  for(int i=0;i<n;i++){
    cout << (ans[i]=='x'?'0':ans[i]);
  }
  cout << endl;
}
