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 main(){
int N, M, i, j; cin >> N >> M; int s[M], c[M];
for(i=0; i<M; i++){ cin >> s[i] >> c[i]; } 
for(i=0; i<1000; i++){
string st=to_string(i);
if(st.size()==N){
int k=0;
for(j=0; j<M; j++){ if(st[s[j]-1]-'0'==c[j]){ k++; } }
if(k==M){ cout << i << "\n"; return 0; }
}
} 
cout << -1 << "\n";
}