F.cpp

// #pragma GCC optimize("Ofast,unroll-loops")
// #pragma GCC target("avx,avx2,fma")

#include <bits/stdc++.h>
using namespace std;

#define ll long long
#define ull unsigned long long
#define dd double
#define ld long double
#define sl(n) scanf("%lld", &n)
#define si(n) scanf("%d", &n)
#define sd(n) scanf("%lf", &n)
#define pll pair <ll, ll>
#define pii pair <int, int>
#define mp make_pair
#define pb push_back
#define all(v) v.begin(), v.end()
#define inf (1LL << 61)
#define loop(i, start, stop, inc) for(ll i = start; i <= stop; i += inc)
#define for1(i, stop) for(ll i = 1; i <= stop; ++i)
#define for0(i, stop) for(ll i = 0; i < stop; ++i)
#define rep1(i, start) for(ll i = start; i >= 1; --i)
#define rep0(i, start) for(ll i = (start-1); i >= 0; --i)
#define ms(n, i) memset(n, i, sizeof(n))
#define casep(n) printf("Case %lld:", ++n)
#define pn printf("\n")
#define pf printf
#define EL '\n'
#define fastio std::ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);

mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
// returns a random ll integer in [l, r] range
inline ll gen_random(ll l, ll r) {
    return uniform_int_distribution<ll>(l, r)(rng);
}

// === DEBUG MACRO STARTS HERE === //
#ifdef LOCALXOX
#define DEBUG
#define SYS_COL system("COLOR")
#endif

int recur_depth = 0;
#ifdef DEBUG
#define dbg(x) {++recur_depth; auto x_=x; --recur_depth; SYS_COL; \
                cerr<<string(recur_depth, '\t')<<"\e[91m"<<__func__<<":" \
                <<__LINE__<<"\t"<<#x<<" = "<<x_<<"\e[39m"<<endl;}

template<typename Ostream, typename Cont>
typename enable_if<is_same<Ostream,ostream>::value,
            Ostream&>::type operator<<(Ostream& os,  const Cont& v) {
	os<<"[";
	for(auto& x:v){os<<x<<", ";}
	return os<<"]";
}
template<typename Ostream, typename ...Ts>
Ostream& operator<<(Ostream& os,  const pair<Ts...>& p){
	return os<<"{"<<p.first<<", "<<p.second<<"}";
}
#else
#define dbg(x)
#endif
// === DEBUG MACRO ENDS HERE === //

#define ff first
#define ss second

const ll sz = 2e5 + 10;

int main()
{
    ll t;
    cin >> t;

    while(t--) {
        ll n, m;
        sl(n), sl(m);

        ll mx = -inf, sum = 0, prec = 0;

        for1(i, n) {
            ll x, y;
            sl(x), sl(y);

            if(i == 1) mx = x;

            ll lo = 1, hi = y, ret = -1;
            while(lo <= hi) {
                ll mid = lo+hi>>1;

                ll cur_b = prec + mid * x;

                if(cur_b >= 0) ret = mid, lo = mid+1;
                else hi = mid-1;
            }
            //dbg(prec*ret + ret*(ret+1)/2 * x);

            if(ret != -1) mx = max(mx, sum + prec*ret + ret*(ret+1)/2 * x);

            sum += prec*y + y*(y+1)/2 * x;
            mx = max(mx, sum);

            prec = prec + x*y;
        }

        pf("%lld\n", mx);
    }

    return 0;
}