import std.stdio;
import std.string, std.conv, std.array, std.algorithm;
import std.uni, std.math, std.container;
import core.bitop, std.datetime;

void main(){
    int N = readln.chomp.to!int;
    auto V = readln.split.to!(int[]);
    int[] dp = new int[](N + 1);

    dp[0] = 0, dp[1] = V[0];
    foreach(i ; 2 .. N + 1){
        dp[i] = max(dp[i - 1], dp[i - 2] + V[i - 1]);
    }

    writeln(dp[N]);
}