#include "bits/stdc++.h"
using namespace std;


#define REP(i,a,b) for(i=a;i<b;i++)
#define rep(i,n) REP(i,0,n)
int N, V[1111], dp[1111];

int main(){
  int i, j, k;

  cin>>N;
  rep(i,N) cin>>V[i];

  dp[0] = V[0];
  dp[1] = max(V[1],V[0]);
  REP(i,2,N) dp[i] = max(dp[i-1], dp[i-2]+V[i]);

  cout<<dp[N-1]<<endl;

  return 0;
}