#include<bits/stdc++.h>
#define ULL unsigned long long
#define int long long
#define endl '\n'
#define debug(a) cout<<#a<<"="<<a<<endl;
#define all(v) v.begin(), v.end()
#define PII pair<int,int>
using namespace std;
constexpr int N =  1 *1e6 + 10,M = 5 * 1e3 + 10,inf = 0x3f3f3f3f;
struct node
{
    double w,v;
    double po; //权重
};
bool cmp(node a,node b) //权重从大到小排序
{
    return a.po > b.po;
}
void solve()
{
    double m;
    int n;
    cin >> m >> n;
    vector<node> c(n); 
    for(int i=0;i<n;i++)
    {
        cin>>c[i].w>>c[i].v;
        c[i].po = c[i].v * 1.0 / c[i].w;
    }
    sort(all(c),cmp);
    double ans = 0;
    for(auto [w,v,po] : c)
    {
        if(m - w <= 0)
        {
            ans += po * m;
            break;
        } 
        m -= w;
        ans += v;
    }
    printf("%.2f\n",ans);
}
signed main()
{
    ios::sync_with_stdio(0);cin.tie(nullptr),cout.tie(nullptr);
    int _=1;
    cin>>_;
    while(_--)
    {
        solve();
    }
    return 0;
}
/**
 *    author: Nijika_jia
 *    created: 2024.10.20 23:08:44
 */