[백준] 10773번 제로

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

public class Main {
    public static void main(String[] args) throws IOException{
    	
    	BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    	
    	int K= Integer.parseInt(br.readLine());
    	Stack<Integer> stack = new Stack<>();
    	for(int i=0; i<K; i++) {
    		int num = Integer.parseInt(br.readLine());
    		
    		if( num!=0 ) {
    			stack.push(num);
    		}else {
    			if(!stack.isEmpty()) {
    				stack.pop();
    			}
    		}
    	}
    	
    	int sum = 0;
    	
    	while(!stack.isEmpty()) {
    		sum += stack.pop();
    	}
    	
    	System.out.println(sum);

    }
}