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,s,c,ans,k;
cin>>n>>m;
int a[n];
for(i=0;i<n;i++){a[i]=-1;}
for(i=0;i<m;i++){cin>>s>>c;
s--;
    if(a[s]!=-1&&a[s]!=c){cout<<"-1";return 0;}
    a[s]=c;
}
if(n==1){cout<<max(0,a[0]);return 0;}
if(n==1&&m==0){cout<<"0";return 0;}
if(!a[0]){cout<<"-1";return 0;}
if(a[0]==-1){a[0]=1;}
k=0;
for(i=0;i<n;i++){a[i]=max(k,a[i]);}
for(i=0;i<n;i++){cout<<a[i];}
    return 0;}