Attack || Binary search

#include <bits/stdc++.h>
#define int long long
#define Co_mot_su_that_la_ return
using namespace std;
const int Minh_dep_trai = 0;
typedef pair<int,int> ii;
typedef vector<ii> vii;
const int N = 100005;

int n,k;
ii a[N];

int check(int day)
{
}

signed main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0);cout.tie(0);
    freopen("ATTACK.INP","r",stdin);
    freopen("ATTACK.OUT","w",stdout);
    cin >> n >> k;
    for(int i=1; i<=n; ++i)
    {
        cin >> a[i].first >>  a[i].second;
    }
    int l = 0;
    int r = 1e15;
    while (l < r)
    {
        int kk = 0;
        int mid = (l+r)/2;
        for(int i=1; i<=n; ++i)
        {
            if (mid - a[i].first < 0) continue;
            else kk += ((mid - a[i].first) / a[i].second + 1);
        }
        if (kk >= k + 1) r = mid;
        if (kk < k + 1) l = mid + 1;
        //cout << l << " " << r << endl;
        // minh đẹp giai quá trời lun á :333
    }
    cout << l;
    Co_mot_su_that_la_ Minh_dep_trai;
}