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;
#define int long long

signed main(){
  int N, M;
  cin >> N >> M;
  int s[1000], c[1000];
  rep(i,M){
    cin >> s[i] >> c[i];
  }
  rep(i,1000){
    bool a = true;
    rep(j,M){
        if(to_string(i)[s[j]-1] != to_string(c[j])[0]){a = false;break;}
    }
    if(a){if(to_string(i).length() == N){cout << i;return 0;}}
  }
  cout << -1;
}

