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 ll long long int
string s;
	



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

if(ans[0]==-1&&n>1)ans[0]=1;
else if(ans[0]==-1)ans[0]=0;

for(ll i=0;i<n;i++)cout<<ans[i];
}


