#!/usr/bin/env python3
# -*- coding: utf-8 -*-

import array


def solve(n, vs):
    if len(vs) < 2:
        return vs[0]
    else:
        dp = array.array("L", [vs[0], max(vs[1], vs[0])])
        for i in range(2, n):
            dp.append(max(dp[i - 1], dp[i - 2] + vs[i]))
        return dp[n - 1]


if __name__ == "__main__":
    n = int(input())
    vs = array.array("I", map(int, input().split()))
    print(solve(n, vs))