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;
cin>>n>>m;
map<int,int>vis,vis1;
int num[n];
for(int i=0; i<n; ++i)
num[i]=0;
int fn(0);
for(int i=0; i<m; ++i)
{
int a,b;
cin>>a>>b;
if(a>n)
fn=1;
if(vis1[a]&&vis[a]!=b)
fn=1;
if(a==1&&b==0&&n>1)
fn=1;
vis[a]=b;
vis1[a]=1;
num[a-1]=b;
}
if(fn==1)
cout<<-1;
else
{
if(m==0&&n>1)
num[0]=1;
if(num[0]==0&&n>1)
num[0]=1;
for(int i=0; i<n; ++i)
cout<<num[i];
}
}
