Help me in solving WELLLEFT problem

help
,
1

My issue

for 3rd test case
20 6 18
the possible number of cases is coming out to be 165, and when i tried it manually, i still find 165 to be the correct ans

the pairs would be
(4,1)
(5,1) (5,2)
(6,1) (6,2) (6,3)

similarly it would go till
…(17, 14)
if we count these pairs it would be
1+2+3+4+…+14 which would be equal to 105

then for a=18, 19 and 20
we would add 20 for each case so additional 60 pairs would be added making the total number of pairs to be 165

My code

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

void solve()
{
    ll n, k, h;
    cin>>n>>k>>h;
    ll count=0, ans;

    ll a=2;
    while (a<=n){
        ans=0;

        if (a>=h){
            count=count+n;
            a++;
            continue;
        }
        
        ll l=1, r=a;
        while (l<=r){
            
            ll mid=(l+r)/2;

            if ((a*k-mid*k)>=h){
                l=mid+1;
                ans=mid;
            }

            else{
                r=mid-1;
            }
        }
        count=count+ans;
        a++;
    }
    cout<<count<<endl;
}

int main(){
    ll t;
    cin>>t;
    while (t--){
        solve();
    }
}

Problem Link: Amphibian Escape Practice Coding Problem

2

there can be pairs like
(17,16)
at time =1 x=1;
at time =2 it will jump out of well
so there will be such test cases that you are missing