#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define ull unsigned long long
#define ld long double
#define inf 0x3f3f3f3f
#define all(x) (x).begin(),(x).end()
#define maxint INT32_MAX
#define minint INT32_MIN
#define maxll INT64_MAX
#define minll INT64_MIN
#define mod  998244353
#define nc() (p1==p2 && (p2=(p1=buf)+fread(buf,1,100000,stdin),p1==p2)?EOF:*p1++)
#pragma GCC optimize(2)
void write(int x);
ll c[120][120];
char *p1,*p2,buf[100000];
int read();
const int N=1e5+10;
int fact[N],infact[N];
struct node{
    ll a,b,c;
    bool operator < (const node& other) const{
        return c<other.c;
    }
};
void solve(){
    ll n,m;
    cin>>n>>m;
    vector<node> v(n+1);
    ll ans=0;
    for(int i=1;i<=n;i++){
        cin>>v[i].a>>v[i].b;
        v[i].c=v[i].a-v[i].b;
        ans+=v[i].a;
    }
    sort(v.begin()+1,v.end());
    ll sum=m-n;
    ll cnt=0;
    //cout<<v[1].a<<' '<<v[1].b<<endl;
    for(int i=1;i<=n;i++){
        if(sum>0){
            if(v[i].c<0){
                sum--;
                ans+=abs(v[i].c);
                cnt++;
            }
        }
    }
    //cout<<cnt<<' '<<ans<<endl;
    if(cnt*2+1==m){
        ans-=v[++cnt].c;
    }
    cout<<ans<<endl;
}

int main() {
    int t=1;
    cin>>t;
    while(t--) solve();
    return 0;
}



void write(int x)
{
    if(x<0)
        putchar('-'),x=-x;
    if(x>9)
        write(x/10);
    putchar(x%10+'0');
    return;
}
int read()
{
    int x=0,f=1;
    char ch=nc();
    while(ch<48||ch>57)
    {
        if(ch=='-')
            f=-1;
        ch=nc();
    }
    while(ch>=48&&ch<=57)
        x=x*10+ch-48,ch=nc();
   	return x*f;
}
// ll ksm(ll a,ll b,ll mod){
//     ll ans=1;
//     a%=mod;
//     while(b>0){
//         if(b&1) ans=ans*a%mod;
//         a=a*a%mod;
//         b>>=1;
//     }
//     return ans;
// }