кузнечик 31

#include <iostream>
#include <cmath>

using namespace std;

int poisk_grass (int N, long long *grass)
{
  long long *sum_grass = new long long[N+1];
  sum_grass[2] = 0;
  sum_grass[3] = grass[0] + grass[2];
  sum_grass[4] = grass[0] + grass[3];

  for (long long k = 5; k <= N; k++)
    sum_grass[k] = max(sum_grass[k-2], sum_grass[k-3]) + grass[k-1];

   return sum_grass[N];
}

int main()
{
  int N;
  cin >> N;

  long long *grass = new long long[N];

  for (long long i = 0; i<N; i++)
  cin >> grass[i];

  if (N == 0)
   cout << 0;
   else if (N == 1 || N == 2)
    cout << grass[0];
   else cout << poisk_grass(N, grass);
}