백준 10773

package baekjoon.구현;

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.Stack;

class Main10773 {

   public static void main(String[] args) throws Exception {
      BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
      Stack<Integer> s = new Stack<>();
      int K = Integer.parseInt(br.readLine());
      int ans = 0;
      int before = -1;
      for (int i = 0; i < K; i++) {
         int n = Integer.parseInt(br.readLine());
         if (n == 0 && i != 0) {
            s.pop();
            continue;
         }
         s.add(n);
      }

      while (!s.isEmpty()) {
         ans += s.pop();
      }
      System.out.println(ans);
   }
}