tj

#include<bits/stdc++.h>
using namespace std;
struct stu{
int n,v;
double jiazhi;
}a[1100];
bool cmp(stu x,stu y){
    return x.jiazhi>y.jiazhi;
}
int main(){
    int t;
    cin>>t;
    while(t--){
        int w,s;
        double zongjia=0;
        cin>>w>>s;
        for(int i=1;i<=s;i++){
            cin>>a[i].n>>a[i].v;
            a[i].jiazhi=a[i].v*1.0/a[i].n;
        }sort(a+1,a+s+1,cmp);
        for(int i=1;i<=s;i++){
            if(w-a[i].n<0){
                zongjia+=a[i].jiazhi*w;
                break;
            }w-=a[i].n,zongjia+=a[i].v;
        }printf("%.2f\n",zongjia);
    }
}