//                      위대한    -    주의 만세!
#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<algorithm>
#include<queue>

#define fi first
#define se second
#define mkp std::make_pair
using llu=long long unsigned;
using ll=long long;
using std::max;
using std::min;
template<class T> void cmax(T&a,T b){a=max(a,b);}
template<class T> void cmin(T&a,T b){a=min(a,b);}

const int NV=5e5;

struct SEG{
    struct SEGN{
        ll mx,tad;
    } tr[NV*8+5];
    void up(int x){
        tr[x].mx=max(tr[x*2].mx,tr[x*2+1].mx);
    }void doadd(int x,ll z){
        tr[x].mx+=z;
        tr[x].tad+=z;
    }void dn(int x){
        if(tr[x].tad){
            doadd(x*2,tr[x].tad);
            doadd(x*2+1,tr[x].tad);
            tr[x].tad=0;
        }
    }void add(int x,int l,int r,int ql,int qr,ll z){
        int mid=l+r>>1;
        if(ql<=l&&r<=qr) return doadd(x,z);
        dn(x);
        if(ql<=mid) add(x*2,l,mid,ql,qr,z);
        if(mid<qr) add(x*2+1,mid+1,r,ql,qr,z);
        up(x);
    }ll que(int x,int l,int r,int ql,int qr){
        int mid=l+r>>1;
        if(ql<=l&&r<=qr) return tr[x].mx;
        dn(x);
        ll ans=-(1ll<<62);
        if(ql<=mid) ans=que(x*2,l,mid,ql,qr);
        if(mid<qr) cmax(ans,que(x*2+1,mid+1,r,ql,qr));
        return ans;
    }void upd(int x,int l,int r,int p,ll z){
        int mid=l+r>>1;
        if(l==r) cmax(tr[x].mx,z);
        else{
            dn(x);
            if(p<=mid) upd(x*2,l,mid,p,z);
            else upd(x*2+1,mid+1,r,p,z);
            up(x);
        }
    }void dfs(int x,int l,int r){
        if(l==r){
            printf("%d %lld\n",l,tr[x].mx);
            return;
        }
        dn(x);
        int mid=l+r>>1;
        dfs(x*2,l,mid);
        dfs(x*2+1,mid+1,r);
    }
};

namespace xm{
    SEG t1,t2;
    int N,M,a[NV+5],b[NV+5],dic[NV*2+5];
    void buildt1(int x,int l,int r){
        int mid=l+r>>1;
        t1.tr[x].tad=0;
        if(l==r) t1.tr[x].mx=-(1ll<<62);
        else{
            buildt1(x*2,l,mid);
            buildt1(x*2+1,mid+1,r);
            t1.up(x);
        }
    }void buildt2(int x,int l,int r){
        int mid=l+r>>1;
        t2.tr[x].tad=0;
        if(l==r) t2.tr[x].mx=-(1ll<<62);
        else{
            buildt2(x*2,l,mid);
            buildt2(x*2+1,mid+1,r);
            t2.up(x);
        }
    }void _(){
        scanf("%d%d",&N,&M);
        for(int i=1;i<=N;++i){
            scanf("%d%d",a+i,b+i);
            dic[++*dic]=a[i];
            dic[++*dic]=a[i]-1;
        }
        dic[++*dic]=0;
        std::sort(dic+1,dic+*dic+1);
        *dic=std::unique(dic+1,dic+*dic+1)-dic-1;
        buildt1(1,1,*dic);
        buildt2(1,1,*dic);
        t1.upd(1,1,*dic,1,0);
        t2.upd(1,1,*dic,1,0);
        //for(int i=1;i<=*dic;++i) printf("%d ",dic[i]); puts("");
        for(int i=1;i<=N;++i){
            ll tv[2];
            for(int x=0;x<=1;++x){
                int tpos=a[i]-x,tpp=std::lower_bound(dic+1,dic+*dic+1,tpos)-dic;
                tv[x]=max(t1.que(1,1,*dic,1,tpp)-tpos*M,
                        t2.que(1,1,*dic,tpp,*dic));
                //printf("tv %d %lld %lld\n",tpp,t1.que(1,1,*dic,1,tpp)-tpos*M,
                //        t2.que(1,1,*dic,tpp,*dic));
            }
            for(int x=0;x<=1;++x){
                int tpos=a[i]-x,tpp=std::lower_bound(dic+1,dic+*dic+1,tpos)-dic;
                t1.upd(1,1,*dic,tpp,tv[x]+tpos*M);
                t2.upd(1,1,*dic,tpp,tv[x]);
            }
            int vp=std::lower_bound(dic+1,dic+*dic+1,a[i])-dic;
            t1.add(1,1,*dic,vp,*dic,b[i]);
            t2.add(1,1,*dic,vp,*dic,b[i]);
            //t2.dfs(1,1,*dic);
        }
        printf("%lld\n",t2.tr[1].mx);
    }
}

int main(){
    int t;
    scanf("%d",&t);
    while(t--) xm::_();
    return 0;
}