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;
using ll=long long;
constexpr ll mod=1e9+7;

int main()
{
  int n,m;
  cin>>n>>m;
  vector<pair<int,int>> sc(m);
  for(auto&& e: sc) 
  {
    cin>>e.first>>e.second;
  }
  int i;
  if(n==3) i=100;
  else if(n==2) i=10;
  else i=0;
  for (; i < 1000; ++i)
  {
    string tmp=to_string(i);
    bool flag=true;
    for(const auto& e: sc) 
    {
      if(tmp[e.first-1]!='0'+e.second) flag=false;
    }
    if(flag)
    {
      cout<<i;
      return 0;
    }
  }
  cout<<-1;
}