Card game

#include <bits/stdc++.h>

using namespace std;

typedef unsigned long long ull;
typedef long long ll;

ll n;
unsigned xs[1000000];
ull s[1000000];

int main(){
    cin >> n;
    for(int i=0; i<n; i++){
        unsigned x;
        cin >> x;
        xs[i] = x;
    }

    if(n<3){
        cout << 0 << endl;
        return 0;
    }
    if(n == 3){
        cout << xs[1] << endl;
        return 0;
    }
    if(n < 5){
        cout << max({xs[1], xs[2], xs[3]}) << endl;
        return 0;
    }

    s[0] = 0;
    s[1] = 0;

    s[2] = (ull)xs[1];
    // s[3] = max(s[2], (ull)xs[2]);
    for(int i=3; i<n; i++){
        s[i] = max(s[i-1], s[i-3]+xs[i-1]);
    }

    auto best = s[n-1];
    cout << best << endl;

    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