#include <iostream>
using namespace std;
const int N=2e5+10;
int a[N],gap[N];
bool dp[N][7];
void solve()
{
int n,k;
cin>>n>>k;
a[0]=0;
for(int i=1;i<=k+1;i++)
{
if(i<=k)
cin>>a[i];
else{
a[i]=n+1;
}
gap[i]=a[i]-a[i-1]-1;
if(gap[i]>2)
{
gap[i]=2-(gap[i]%2);
}
}
// gap[i]<=2
for(int i=0;i<=k+1;i++)dp[i][0]=dp[i][1]=dp[i][2]=dp[i][3]=0;
dp[1][gap[1]]=1;
for(int i=2;i<=k+1;i++)
{
if(dp[i-1][0])
{
dp[i][gap[i]]=1;
}
if(dp[i-1][1] and gap[i]>=1)
{
dp[i][gap[i]-1]=1;
}
if(dp[i-1][2] and gap[i]>=2)
{
dp[i][gap[i]-2]=1;
}
}
int r=-1;
if(dp[k+1][0])r=0;
cout<<r<<endl;
}
int main()
{
ios::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
int t;
cin>>t;
while(t--)
{
solve();
}
}
