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 a[8];
int main()
{
    memset(a,-1,sizeof(a));
    int n,m;cin>>n>>m;
    int x,y;
    while(m--)
    {
        cin>>x>>y;
        if(a[x]!=-1&&a[x]!=y) return cout<<"-1",0;
        a[x]=y;
    }
    if(n!=1&&a[1]==0) return cout<<"-1",0;
    for(int i=1;i<=n;i++)
    {
        if(a[i]!=-1) cout<<a[i];
        else if(n==1||i!=1) cout<<0;
        else cout<<1;
    }
}
