import std.algorithm, std.array, std.container, std.range;
import std.string, std.conv, std.math;
import std.stdio, std.typecons;

void main()
{
  auto n = readln.chomp.to!int;
  auto vi = readln.split.map!(to!int);

  if (n == 1) {
    writeln(vi[0]);
  } else {
    auto dp = new long[n];
    dp[0] = vi[0];
    dp[1] = max(vi[0], vi[1]);

    foreach (i; 2..n) {
      dp[i] = max(dp[i - 2] + vi[i], dp[i - 1]);
    }

    writeln(dp[n - 1]);
  }
}