import java.util.Scanner;

public class No1765 {

	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int N = scan.nextInt();
		int[] A = new int[N-1];
		for (int i=0; i < N-1; i++) {
			A[i] = scan.nextInt();
		}
		scan.close();
		int m0 = 0, m1 = 0, cnt = 0;
		for (int a : A) {
			if (a == 1) {
				cnt += 1 + m1;
				m0 = 1 + m1;
				m1 = 0;
			} else {
				cnt += m0;
				m1 = m0;
				m0 = 0;
			}
		}
		System.out.println(cnt);
	}

}