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;
#define rep(i,n) for(int i=1;i<=n;i++)
int main(){int ans[4];int n,m,s,c;cin>>n>>m;rep(i,4)ans[i]=10;rep(i,m){cin>>s>>c;if(ans[s]==10||ans[s]==c)ans[s]=c;else{cout<<-1;return 0;}}if(n!=1&&ans[1]==0){cout<<-1;return 0;}rep(i,n)if(ans[i]==10)ans[i]=0;if(n!=1&&ans[1]==0)ans[1]++;rep(i,n)cout<<ans[i];}