#include<iostream>
#include<algorithm>
#define lc(u) u<<1
#define rc(u) u<<1|1
#define int long long
using namespace std;
const int N=5e5+5,inf=1e18;
int t,n,k;
int a[N],b[N],g[N],h[N],dp[N],v[N];
int tr[N<<2][2],lz[N<<2];
void pushup(int u){
	tr[u][0]=max(tr[lc(u)][0],tr[rc(u)][0]);
	tr[u][1]=max(tr[lc(u)][1],tr[rc(u)][1]);
}
void pushdown(int u){
	if(lz[u]){
		lz[lc(u)]+=lz[u];
		lz[rc(u)]+=lz[u];
		tr[lc(u)][0]+=lz[u];
		tr[rc(u)][0]+=lz[u];
		tr[lc(u)][1]+=lz[u];
		tr[rc(u)][1]+=lz[u];
		lz[u]=0;
	}
}
void build(int u,int l,int r){
	if(l==r){
		tr[u][0]=tr[u][1]=-inf;
		lz[u]=0;
		return;
	}
	int mid=(l+r)>>1;
	build(lc(u),l,mid);
	build(rc(u),mid+1,r);
	pushup(u);
}
int query(int u,int l,int r,int L,int R,int op){
	if(L<=l&&r<=R) return tr[u][op];
	pushdown(u);
	int mid=(l+r)>>1,ans=-inf;
	if(L<=mid) ans=max(ans,query(lc(u),l,mid,L,R,op));
	if(mid<R) ans=max(ans,query(rc(u),mid+1,r,L,R,op));
	pushup(u);
	return ans;
}
void update(int u,int l,int r,int L,int R,int v){
	if(L<=l&&r<=R){
		tr[u][0]+=v;
		tr[u][1]+=v;
		lz[u]+=v;
		return;
	}
	pushdown(u);
	int mid=(l+r)>>1;
	if(L<=mid) update(lc(u),l,mid,L,R,v);
	if(mid<R) update(rc(u),mid+1,r,L,R,v);
	pushup(u);
}
void modify(int u,int l,int r,int x,int w){
	if(l==x&&r==x){
		tr[u][0]=w;
		tr[u][1]=w+k*v[l];
		return;
	}
	pushdown(u);
	int mid=(l+r)>>1;
	if(mid>=x) modify(lc(u),l,mid,x,w);
	else modify(rc(u),mid+1,r,x,w);
	pushup(u);
}
signed main(){
	ios::sync_with_stdio(0); 
	cin>>t;
	while(t--){
		cin>>n>>k;
		for(int i=1;i<=n;i++) cin>>a[i]>>b[i];
		for(int i=1;i<=n;i++) g[i]=a[i]-(b[i]<0);
		for(int i=1;i<=n;i++) h[i]=g[i];
		h[n+1]=0;
		sort(h+1,h+n+1);
		int m=unique(h+1,h+n+1)-h-1;
		for(int i=1;i<=n;i++){
			int x=lower_bound(h+1,h+m+1,g[i])-h;
			v[x]=g[i];
			g[i]=x;
		}
		build(1,1,m);
		for(int i=1;i<=n;i++) dp[i]=-inf;
		for(int i=1;i<=n;i++){
			int u=g[i];
			if(b[i]>=0){
				dp[u]=max(0ll,query(1,1,m,1,u,1))-k*v[u];
				modify(1,1,m,u,dp[u]);
				update(1,1,m,u,m,b[i]);
			}
			else{
				dp[u]=query(1,1,m,u,m,0);
				modify(1,1,m,u,dp[u]);
				update(1,1,m,u+1,m,b[i]);
			}
		}
		cout<<max(0ll,tr[1][0])<<"\n";
	}
	return 0;
}