#include<bits/stdc++.h>
using namespace std;

struct jin {
	double zl,jz,xjb;
}a[100000];

bool cmp (jin x,jin y) {
	if (x.xjb>y.xjb) {
		return 1;
	} else {
		return 0;
	}
}

int main () {
	int k; cin >> k;
	for (int i = 1; i <= k; i++) {
		int w,n; double sum=0; cin >> w >> n;
		for (int j = 1; j <= n; j++) {
			cin >> a[j].zl >> a[j].jz;
			a[j].xjb=a[j].jz/a[j].zl;
		}
		sort(a+1,a+1+n,cmp);
		int l=1;
		while (w&&l<=n) {
			if (a[l].zl<=w) {
				w -= a[l].zl;
				sum += a[l].jz;
			} else {
				sum += w*a[l].xjb; w=0;
				break;
			}
			l++;
		}
		printf("%.2f\n",sum);
	}
	return 0;
}