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 toreru = 0, torenai = 0;

    foreach(v ; V){
        int tmp = toreru;
        toreru = torenai;
        torenai = max(torenai, tmp + v);
    }

    writeln(max(toreru, torenai));
}