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 X[3]={-1,-1,-1};
bool f=true;
int main()
{
  int N,M;
  cin>>N>>M;
  while(M--)
  {
    int A,B;
    cin>>A>>B;
    A--;
    if(!A&&!B&&N>1)
      f=false;
    if(X[A]!=-1&&X[A]!=B)
      f=false;
    X[A]=B;
  }
  for(int i=1;i<N;i++)
    if(X[i]==-1)
      X[i]=0;
  if(X[0]==-1&&N>1)
    X[0]=1;
  if(X[0]==-1&&N<=1)
    X[0]=0;
  if(f)
  {
    for(int i=0;i<N;i++)
      cout<<X[i];
  }
  else puts("-1");
  return 0;
}