Card game

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

void out(const vl &a)
{
    for(auto x : a)
        cerr << x << " ";
    cerr << "\n";
}

int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0); cout.tie(0);

    ll n, i;
    cin >> n;
    vl a(n), ans(n, 0);
    for(i = 0; i < n; i++)
        cin >> a[i];
    if(n < 5)
    {
        if(n < 3)
            cout << 0;
        if(n == 3)
            cout << a[1];
        if(n == 4)
            cout << max(a[1], a[2]);
        return 0;
    }

    ans[1] = a[1]; ans[2] = max(a[1], a[2]);
    for(i = 3; i < n - 1; i++)
        ans[i] = max({ans[i - 1], ans[i - 2], ans[i - 3] + a[i]});
    //out(ans);
    cout << ans[n - 2];

    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

Test 13

Verdict: ACCEPTED

Test 14

Verdict: ACCEPTED

Test 15

Verdict: ACCEPTED