Help, NNLT nào cx đc

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

int main() {
    ll n;
    cin>>n;
    vector<int>a(n+5);
    vector<int>dp(n+5,0);
    for (int i=0;i<n;++i) {
        cin>>a[i];
    }
    if(n==1) cout<<a[0];
    else if(n==2) cout<<a[0]+a[1];
    else{
        dp[0]=a[0];
        dp[1]=a[0]+a[1];
        dp[2]=max(a[0]+a[2],max(a[0]+a[1],a[1]+a[2]));
        for (int i=3; i<n; ++i){
            dp[i]=max(dp[i-1],max(dp[i-2]+a[i],dp[i-3]+a[i]+a[i-1]));
        }cout<<dp[n-1];
    }
    return 0;
}