#include <stdio.h>
unsigned long long DP[100001][3];
unsigned long long answer = 0;
unsigned int data[100001];
int main() {
  int N, i;
  scanf("%d", &N);

  for (i = 1; i <= N; i++) {
    scanf("%d", &data[i]);
  }
 DP[1][1] = data[1];
 DP[2][1] = data[2];
 DP[2][2] = DP[1][1] + data[2];

 for (int k = 3; k <= N; k++) {
   DP[k][0] = DP[k - 1][2];
   DP[k][1] = DP[k - 1][0] + data[k];
   DP[k][2] = DP[k - 1][1] + data[k];
 }
 answer = (DP[N][0] > DP[N][1]) ? DP[N][0] : DP[N][1];
 if (answer < DP[N][2]) answer = DP[N][2];

  printf("%lld\n", answer);
  return 0;
}