#include<bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

#define openr() freopen("input.txt","r",stdin)
#define openw() freopen("output.txt","w",stdout)
#define mp make_pair
#define fi first
#define se second
#define int long long int

using namespace std;
using namespace __gnu_pbds;
template <typename T>
using ordered_set=tree<T,null_type,less<T>,rb_tree_tag,tree_order_statistics_node_update>;

const int inf = 1e18;
const int maxn = 2e6;
const int mod = 1e9 + 7;

/*
    find_by_order(k)
    order_of_key(k)
*/




void show() {
    int n,m;    cin>>n>>m;
    deque<int>v;
    int sum = 0;
    int res=0;
    for(int i=1;i<=n;i++) {
        int temp1,temp2;
        cin>>temp1>>temp2;
        v.push_back(temp1-temp2);
        res += temp1;
    }
    sum= res;
    sort(v.begin(), v.end());
    for(int i=1;i<n;i++) {
        // i flip
        // i*2 spaces
        if(i*2 + n-i <= m && (n-i) != 1) {
            sum-= v.front();
            v.pop_front();
            res= max(res, sum);
        }
    }
    if(n*2 -1 <= m) {
        while(v.size()) {
            sum -= v.front();
            v.pop_front();
        }
        res= max(res, sum);
    }
    cout<<res;
}

int32_t main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    //openr();
    int tc; cin>>tc;
    while(tc--) {
        show();
        cout<<"\n";
    }
    return 0;
}