# include <bits/stdc++.h>
using namespace std;
const double g=10;
pair<double,double> solve(double A,double B,double C)
{
	double delta=B*B-4*A*C;
	return {(-B-sqrt(delta))/2/A,(-B+sqrt(delta))/2/A};
}
int main()
{
	int T;
	cin>>T;
	while(T--)
	{
		double v,L=0,R=1e18;
		int n,x,y;
		scanf("%lf%d",&v,&n);
		for(int i=1;i<=n;i++)
		{
			scanf("%d%d",&x,&y);
			auto seg=solve(g*x*x/2/v/v,-x,y+g*x*x/2/v/v);
			L=max(L,seg.first);R=min(R,seg.second);
		}
		printf("%.5lf\n",(L+R)/2);
	}
	return 0;
}