#include <cstdio>
#include <algorithm>
using namespace std;

class range {private: struct I{int x;int operator*(){return x;}bool operator!=(I& lhs){return x<lhs.x;}void operator++(){++x;}};I i,n;
public:range(int n):i({0}),n({n}){}range(int i,int n):i({i}),n({n}){}I& begin(){return i;}I& end(){return n;}};

int main(void) {
  int n; scanf("%d", &n);
  vector<int> v(n);
  for(int i : range(n)) { scanf("%d", &v[i]); }
  if(n == 1) { printf("%d\n", v[0]); return 0; }
  vector<int> dp(n);
  dp[0] = v[0];
  dp[1] = max(v[0], v[1]);
  for(int i : range(2, n)) {
    dp[i] = max(dp[i-1], dp[i-2] + v[i]);
  }
  printf("%d\n", dp[n-1]);
  return 0;
}