package yukicoder;

import java.util.Scanner;

public class No45 {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		final int N = sc.nextInt();
		int[] sara = new int[N];
		for (int i = 0; i < N; i++) {
			sara[i] = sc.nextInt();
		}
		int sum = 0;
		boolean[] b2 = new boolean[N];
		boolean end = false;
		while(end == false){
			for(int i = 0; i < N; i++){
				if(b2[i] == true)
					continue;
				boolean b = false;
				if(i + 1 < N){
					if(sara[i] < sara[i + 1] && b2[i + 1] == false){
						b = true;
					}
				}
				if(i + 2 < N){
					if(sara[i] < sara[i + 2] && b2[i + 2] == false){
						b = true;
					}
				}
				if(b==false){
					sum += sara[i];
					if(i-1 >= 0){
						b2[i - 1] = true;
					}
					b2[i] = true;
					if(i + 1 < N){
						b2[i + 1] = true;
					}
					i++;
				}
			}
			for(int i = 0; i < N; i++){
				if(b2[i] == false){
					end = false;
					break;
				}
				end = true;
			}
			if(end == true){
				System.out.println(sum);
			}
		}
	}
}