#include<bits/stdc++.h>
#define ll long long
using namespace std;
const int N = 1e6 + 10;
ll n, m, lsh[N], ans, tot, a[N], b[N];
struct tree{
	int l, r;
	ll maxn1, maxn2, la1, la2, tp;
}tr[4 * N];
void pp(int id){
	tr[id].maxn1 = max(tr[2 * id].maxn1, tr[2 * id + 1].maxn1);
	tr[id].maxn2 = max(tr[2 * id].maxn2, tr[2 * id + 1].maxn2);
}
void add(int id, ll x){
	tr[id].maxn1 += x, tr[id].maxn2 += x, tr[id].la1 += x;
}
void chg1(int id, ll x){
	tr[id].maxn1 = x, tr[id].maxn2 = x + m * lsh[tr[id].r], tr[id].la1 = 0, tr[id].la2 = x, tr[id].tp = 1;
}
void chg2(int id, ll x){
	tr[id].maxn1 = x - m * lsh[tr[id].l], tr[id].maxn2 = x, tr[id].la1 = 0, tr[id].la2 = x, tr[id].tp = 2;
}
void pd(int id){
	if(tr[id].tp == 1){
		chg1(2 * id, tr[id].la2);
		chg1(2 * id + 1, tr[id].la2);
		tr[id].la2 = tr[id].tp = 0;
	}
	if(tr[id].tp == 2){
		chg2(2 * id, tr[id].la2);
		chg2(2 * id + 1, tr[id].la2);
		tr[id].la2 = tr[id].tp = 0;
	}
	add(2 * id, tr[id].la1);
	add(2 * id + 1, tr[id].la1);
	tr[id].la1 = 0;
}
void build(int l, int r, int id){
	tr[id].l = l, tr[id].r = r, tr[id].la1 = tr[id].la2 = tr[id].tp = 0;
	if(l == r){
		tr[id].maxn1 = -m * lsh[l], tr[id].maxn2 = 0;
		return;
	}
	int mid = (l + r) >> 1;
	build(l, mid, 2 * id);
	build(mid + 1, r, 2 * id + 1);
	pp(id);
}
ll query(int id, int pos){
	if(tr[id].l == tr[id].r)
		return tr[id].maxn1;
	pd(id);
	int mid = (tr[id].l + tr[id].r) >> 1;
	if(pos <= mid)
		return query(2 * id, pos);
	return query(2 * id + 1, pos);
}
bool update1(int id, int pos, ll x){
	if(tr[id].r <= pos){
		if(tr[id].maxn1 <= x){
			chg1(id, x);
			return 0;
		}
		while(tr[id].l != tr[id].r){
			pd(id);
			if(tr[2 * id + 1].maxn1 <= x){
				chg1(2 * id + 1, x);
				id = 2 * id;
			}
			else
				id = 2 * id + 1;
		}
		if(tr[id].maxn1 <= x)
			chg1(id, x);
		return 1;
	}
	pd(id);
	int mid = (tr[id].l + tr[id].r) >> 1;
	if(pos > mid && update1(2 * id + 1, pos, x))
		return 1;
	bool t = update1(2 * id, pos, x);
	pp(id);
	return t;
}
bool update2(int id, int pos, ll x){
	if(tr[id].l >= pos){
		if(tr[id].maxn2 <= x){
			chg2(id, x);
			return 0;
		}
		while(tr[id].l != tr[id].r){
			pd(id);
			if(tr[2 * id].maxn2 <= x){
				chg2(2 * id, x);
				id = 2 * id + 1;
			}
			else
				id = 2 * id;
		}
		if(tr[id].maxn2 <= x)
			chg2(id, x);
		return 1;
	}
	pd(id);
	int mid = (tr[id].l + tr[id].r) >> 1;
	if(pos <= mid && update2(2 * id, pos, x))
		return 1;
	bool t = update2(2 * id + 1, pos, x);
	pp(id);
	return t;
}
void update3(int id, int pos, ll x){
	if(tr[id].l >= pos)
		return add(id, x);
	pd(id);
	int mid = (tr[id].l + tr[id].r) >> 1;
	if(pos <= mid)
		update3(2 * id, pos, x);
	update3(2 * id + 1, pos, x);
	pp(id);
}
int main(){
//	freopen("input.txt", "r", stdin);
//	freopen("output.txt", "w", stdout);
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int Cases;
	cin >> Cases;
	while(Cases--){
		cin >> n >> m;
		tot = 0;
		for(int i = 1; i <= n; i++){
			cin >> a[i] >> b[i];
			lsh[++tot] = a[i], lsh[++tot] = a[i] - 1;
		}
		sort(lsh, lsh + tot + 1);
		tot = unique(lsh, lsh + tot + 1) - lsh - 1, ans = 0;
		build(0, tot, 1);
		for(int i = 1; i <= n; i++){
			a[i] = lower_bound(lsh, lsh + tot + 1, a[i]) - lsh;
			update3(1, a[i], b[i]);
			if(b[i] >= 0)
				update1(1, a[i] - 1, query(1, a[i]));
			else
				update2(1, a[i], query(1, a[i] - 1) + m * lsh[a[i] - 1]);
			ans = max(ans, tr[1].maxn1);
		}
		cout << ans << "\n";
	}
	return 0;
}