Equilateral numbers

#include <bits/stdc++.h>
#include <iostream>
 
#define int long long
using namespace std;
 
bool s(int a){
    int b = 1 + 8 * a;
    int sq = sqrt(b);
    return (sq * sq == b);
}
 
 
void solve()
{
    int n;
    cin >> n;
    bool k = false;
    if (s(n))
        cout << 1;
    else
    {
        int a = 1;
        while ((a * (a+1)) / 2 < n)
        {
            if (s(n-(a*(a+1)) / 2))
            {
                k = true;
                break;
            }
            a++;
        }
        if (k)
            cout << 2;
        else
            cout << 3;
 
    }
}
 
signed main()
{
    solve();
    return 0;
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED