# coding: utf-8


def main():
    n = int(input())
    v = list(map(int, input().split()))

    ans = []

    while(len(v) > 0):
        ans.append(max(v))
        index = (max(enumerate(v), key=lambda x: x[1])[0])

        begin = index - 1 if index > 0 else index
        end = index + 1 if index < len(v) else index
        """
        if index > 0:
            begin = index - 1
        else:
            begin = index

        if index < len(v):
            end = index + 1
        else:
            end = index
        """

        del v[begin:end+1]

    print(sum(ans))


if __name__ == '__main__':
    main()